diff --git a/pydov/types/abstract.py b/pydov/types/abstract.py
index e0398f9..b5217b0 100644
--- a/pydov/types/abstract.py
+++ b/pydov/types/abstract.py
@@ -520,8 +520,7 @@ class AbstractDovType(AbstractCommon):
 
         """
         fields = self.get_field_names(return_fields)
-        ownfields = self.get_field_names(include_subtypes=False,
-                                         return_fields=return_fields)
+        ownfields = self.get_field_names(include_subtypes=False)
         subfields = [f for f in fields if f not in ownfields]
 
         if len(subfields) > 0:

Cannot use fields from a subtype as return fields.
* PyDOV version: master
* Python version: 3.6
* Operating System: Windows 10

### Description

Specifying a field from a subtype as return field gives an error if the resulting dataframe is non-empty.

### What I Did

```
import pydov.search.boring
from owslib.fes import PropertyIsEqualTo

bs = pydov.search.boring.BoringSearch()

bs.search(query=query, return_fields=('pkey_boring',))
                                         pkey_boring
0  https://www.dov.vlaanderen.be/data/boring/2004...

bs.search(query=query, return_fields=('pkey_boring', 'boormethode'))
Traceback (most recent call last):
  File "<input>", line 1, in <module>
  File "C:\Projecten\PyDov\pydov_git\pydov\search\boring.py", line 114, in search
    columns=Boring.get_field_names(return_fields))
  File "C:\Users\rhbav33\python_virtualenvs\3.6_dev\lib\site-packages\pandas\core\frame.py", line 364, in __init__
    data = list(data)
  File "C:\Projecten\PyDov\pydov_git\pydov\types\abstract.py", line 467, in to_df_array
    result = item.get_df_array(return_fields)
  File "C:\Projecten\PyDov\pydov_git\pydov\types\abstract.py", line 524, in get_df_array
    return_fields=return_fields)
  File "C:\Projecten\PyDov\pydov_git\pydov\types\abstract.py", line 386, in get_field_names
    raise InvalidFieldError("Unknown return field: '%s'" % rf)
pydov.util.errors.InvalidFieldError: Unknown return field: 'boormethode'
```

diff --git a/tests/test_search_boring.py b/tests/test_search_boring.py
index 8da9d97..d31f72a 100644
--- a/tests/test_search_boring.py
+++ b/tests/test_search_boring.py
@@ -365,6 +365,36 @@ class TestBoringSearch(AbstractTestSearch):
         assert list(df) == ['pkey_boring', 'boornummer', 'diepte_boring_tot',
                             'datum_aanvang']
 
+    def test_search_returnfields_subtype(self, mp_remote_wfs_feature,
+                                         boringsearch):
+        """Test the search method with the query parameter and a selection of
+        return fields, including fields from a subtype.
+
+        Test whether the output dataframe contains only the selected return
+        fields.
+
+        Parameters
+        ----------
+        mp_remote_wfs_feature : pytest.fixture
+            Monkeypatch the call to get WFS features.
+        boringsearch : pytest.fixture returning pydov.search.BoringSearch
+            An instance of BoringSearch to perform search operations on the DOV
+            type 'Boring'.
+
+        """
+        query = PropertyIsEqualTo(propertyname='boornummer',
+                                  literal='GEO-04/169-BNo-B1')
+
+        df = boringsearch.search(query=query,
+                                 return_fields=('pkey_boring', 'boornummer',
+                                                'diepte_methode_van',
+                                                'diepte_methode_tot'))
+
+        assert type(df) is DataFrame
+
+        assert list(df) == ['pkey_boring', 'boornummer', 'diepte_methode_van',
+                            'diepte_methode_tot']
+
     def test_search_returnfields_order(self, mp_remote_wfs_feature,
                                        boringsearch):
         """Test the search method with the query parameter and a selection of
diff --git a/tests/test_search_grondwaterfilter.py b/tests/test_search_grondwaterfilter.py
index 5916163..d6c4ff7 100644
--- a/tests/test_search_grondwaterfilter.py
+++ b/tests/test_search_grondwaterfilter.py
@@ -380,6 +380,37 @@ class TestGrondwaterFilterSearch(AbstractTestSearch):
 
         assert list(df) == ['pkey_filter', 'gw_id', 'filternummer']
 
+    def test_search_returnfields_subtype(self, mp_remote_wfs_feature,
+                                         grondwaterfiltersearch):
+        """Test the search method with the query parameter and a selection of
+        return fields, including fields from a subtype.
+
+        Test whether the output dataframe contains only the selected return
+        fields.
+
+        Parameters
+        ----------
+        mp_remote_wfs_feature : pytest.fixture
+            Monkeypatch the call to get WFS features.
+        grondwaterfiltersearch : pytest.fixture returning
+            pydov.search.GrondwaterFilterSearch
+            An instance of GrondwaterFilterSearch to perform search operations
+            on the DOV type 'GrondwaterFilter'.
+
+        """
+        query = PropertyIsEqualTo(propertyname='filterfiche',
+                                  literal='https://www.dov.vlaanderen.be/'
+                                          'data/filter/2003-004471')
+
+        df = grondwaterfiltersearch.search(
+            query=query, return_fields=('pkey_filter', 'gw_id',
+                                        'filternummer', 'peil_mtaw'))
+
+        assert type(df) is DataFrame
+
+        assert list(df) == ['pkey_filter', 'gw_id', 'filternummer',
+                            'peil_mtaw']
+
     def test_search_returnfields_order(self, mp_remote_wfs_feature,
                                        grondwaterfiltersearch):
         """Test the search method with the query parameter and a selection of

pip install -e .
parse_log_pytest
requirements.txt
pytest pytest-cov pytest-runner coverage Sphinx sphinx_rtd_theme numpydoc
3.6
requirements.txt
pytest --no-header -rA --tb=line --color=no -p no:cacheprovider -W ignore::DeprecationWarning
alabaster==0.7.13
attrs==22.2.0
Babel==2.11.0
certifi==2021.5.30
charset-normalizer==2.0.12
coverage==6.2
dataclasses==0.8
docutils==0.18.1
idna==3.10
imagesize==1.4.1
importlib-metadata==4.8.3
iniconfig==1.1.1
Jinja2==3.0.3
lxml==5.3.1
MarkupSafe==2.0.1
numpy==1.19.5
numpydoc==1.1.0
OWSLib==0.31.0
packaging==21.3
pandas==1.1.5
pluggy==1.0.0
py==1.11.0
-e git+https://github.com/DOV-Vlaanderen/pydov.git@68d5a639fa77fb9b03a89ca11a3dc49b1c823b27#egg=pydov
Pygments==2.14.0
pyparsing==3.1.4
pytest==7.0.1
pytest-cov==4.0.0
pytest-runner==5.3.2
python-dateutil==2.9.0.post0
pytz==2025.2
PyYAML==6.0.1
requests==2.27.1
six==1.17.0
snowballstemmer==2.2.0
Sphinx==5.3.0
sphinx-rtd-theme==2.0.0
sphinxcontrib-applehelp==1.0.2
sphinxcontrib-devhelp==1.0.2
sphinxcontrib-htmlhelp==2.0.0
sphinxcontrib-jquery==4.1
sphinxcontrib-jsmath==1.0.1
sphinxcontrib-qthelp==1.0.3
sphinxcontrib-serializinghtml==1.1.5
tomli==1.2.3
typing_extensions==4.1.1
urllib3==1.26.20
zipp==3.6.0

name: pydov
channels:
  - defaults
  - https://repo.anaconda.com/pkgs/main
  - https://repo.anaconda.com/pkgs/r
  - conda-forge
dependencies:
  - _libgcc_mutex=0.1=main
  - _openmp_mutex=5.1=1_gnu
  - ca-certificates=2025.2.25=h06a4308_0
  - certifi=2021.5.30=py36h06a4308_0
  - ld_impl_linux-64=2.40=h12ee557_0
  - libffi=3.3=he6710b0_2
  - libgcc-ng=11.2.0=h1234567_1
  - libgomp=11.2.0=h1234567_1
  - libstdcxx-ng=11.2.0=h1234567_1
  - ncurses=6.4=h6a678d5_0
  - openssl=1.1.1w=h7f8727e_0
  - pip=21.2.2=py36h06a4308_0
  - python=3.6.13=h12debd9_1
  - readline=8.2=h5eee18b_0
  - setuptools=58.0.4=py36h06a4308_0
  - sqlite=3.45.3=h5eee18b_0
  - tk=8.6.14=h39e8969_0
  - wheel=0.37.1=pyhd3eb1b0_0
  - xz=5.6.4=h5eee18b_1
  - zlib=1.2.13=h5eee18b_1
  - pip:
      - alabaster==0.7.13
      - attrs==22.2.0
      - babel==2.11.0
      - charset-normalizer==2.0.12
      - coverage==6.2
      - dataclasses==0.8
      - docutils==0.18.1
      - idna==3.10
      - imagesize==1.4.1
      - importlib-metadata==4.8.3
      - iniconfig==1.1.1
      - jinja2==3.0.3
      - lxml==5.3.1
      - markupsafe==2.0.1
      - numpy==1.19.5
      - numpydoc==1.1.0
      - owslib==0.31.0
      - packaging==21.3
      - pandas==1.1.5
      - pluggy==1.0.0
      - py==1.11.0
      - pygments==2.14.0
      - pyparsing==3.1.4
      - pytest==7.0.1
      - pytest-cov==4.0.0
      - pytest-runner==5.3.2
      - python-dateutil==2.9.0.post0
      - pytz==2025.2
      - pyyaml==6.0.1
      - requests==2.27.1
      - six==1.17.0
      - snowballstemmer==2.2.0
      - sphinx==5.3.0
      - sphinx-rtd-theme==2.0.0
      - sphinxcontrib-applehelp==1.0.2
      - sphinxcontrib-devhelp==1.0.2
      - sphinxcontrib-htmlhelp==2.0.0
      - sphinxcontrib-jquery==4.1
      - sphinxcontrib-jsmath==1.0.1
      - sphinxcontrib-qthelp==1.0.3
      - sphinxcontrib-serializinghtml==1.1.5
      - tomli==1.2.3
      - typing-extensions==4.1.1
      - urllib3==1.26.20
      - zipp==3.6.0
prefix: /opt/conda/envs/pydov

tests/test_search_boring.py::TestBoringSearch::test_search_returnfields_subtype
tests/test_search_grondwaterfilter.py::TestGrondwaterFilterSearch::test_search_returnfields_subtype
tests/test_search_boring.py::TestBoringSearch::test_get_fields tests/test_search_boring.py::TestBoringSearch::test_search_both_location_query tests/test_search_boring.py::TestBoringSearch::test_search tests/test_search_boring.py::TestBoringSearch::test_search_returnfields tests/test_search_boring.py::TestBoringSearch::test_search_returnfields_order tests/test_search_boring.py::TestBoringSearch::test_search_wrongreturnfields tests/test_search_boring.py::TestBoringSearch::test_search_wrongreturnfieldstype tests/test_search_boring.py::TestBoringSearch::test_search_query_wrongfield tests/test_search_boring.py::TestBoringSearch::test_search_query_wrongfield_returnfield tests/test_search_boring.py::TestBoringSearch::test_search_extrareturnfields tests/test_search_boring.py::TestBoringSearch::test_search_xmlresolving tests/test_search_grondwaterfilter.py::TestGrondwaterFilterSearch::test_get_fields tests/test_search_grondwaterfilter.py::TestGrondwaterFilterSearch::test_search_both_location_query tests/test_search_grondwaterfilter.py::TestGrondwaterFilterSearch::test_search tests/test_search_grondwaterfilter.py::TestGrondwaterFilterSearch::test_search_returnfields tests/test_search_grondwaterfilter.py::TestGrondwaterFilterSearch::test_search_returnfields_order tests/test_search_grondwaterfilter.py::TestGrondwaterFilterSearch::test_search_wrongreturnfields tests/test_search_grondwaterfilter.py::TestGrondwaterFilterSearch::test_search_wrongreturnfieldstype tests/test_search_grondwaterfilter.py::TestGrondwaterFilterSearch::test_search_query_wrongfield tests/test_search_grondwaterfilter.py::TestGrondwaterFilterSearch::test_search_query_wrongfield_returnfield tests/test_search_grondwaterfilter.py::TestGrondwaterFilterSearch::test_search_extrareturnfields tests/test_search_grondwaterfilter.py::TestGrondwaterFilterSearch::test_search_xmlresolving
pydov/types/abstract.py
pydov/types/abstract.py