BUG: inconsistent replace
- [x] I have checked that this issue has not already been reported.

- [x] I have confirmed this bug exists on the latest version of pandas.

- [x] (optional) I have confirmed this bug exists on the master branch of pandas.

---

#### Problem description

```python
>>> pd.DataFrame([[1,1.0],[2,2.0]]).replace(1.0, 5)
   0    1
0  1  5.0
1  2  2.0

>>> pd.DataFrame([[1,1.0],[2,2.0]]).replace(1, 5)
   0    1
0  5  5.0
1  2  2.0
```

#### Problem description

Maybe I don't understand somethink or this is just non-sens

#### Expected Output


```python
>>> pd.DataFrame([[1,1.0],[2,2.0]]).replace(1.0, 5)
   0    1
0  1  5.0
1  2  2.0

>>> pd.DataFrame([[1,1.0],[2,2.0]]).replace(1, 5)
   0    1
0  5  1.0
1  2  2.0
```
Or
```python
>>> pd.DataFrame([[1,1.0],[2,2.0]]).replace(1.0, 5)
   0    1
0  5  5.0
1  2  2.0

>>> pd.DataFrame([[1,1.0],[2,2.0]]).replace(1, 5)
   0    1
0  5  5.0
1  2  2.0
```

#### Output of ``pd.show_versions()``

<details>

INSTALLED VERSIONS
------------------
commit           : None
python           : 3.6.9.final.0
python-bits      : 64
OS               : Linux
OS-release       : 5.3.0-62-generic
machine          : x86_64
processor        : x86_64
byteorder        : little
LC_ALL           : None
LANG             : en_US.UTF-8
LOCALE           : en_US.UTF-8

pandas           : 1.0.5
numpy            : 1.19.0
pytz             : 2020.1
dateutil         : 2.8.1
pip              : 20.1.1
setuptools       : 49.2.0
Cython           : None
pytest           : 5.4.3
hypothesis       : None
sphinx           : 3.1.1
blosc            : None
feather          : None
xlsxwriter       : None
lxml.etree       : None
html5lib         : None
pymysql          : None
psycopg2         : None
jinja2           : 2.11.2
IPython          : 7.15.0
pandas_datareader: None
bs4              : None
bottleneck       : None
fastparquet      : None
gcsfs            : 0.6.2
lxml.etree       : None
matplotlib       : 3.2.2
numexpr          : 2.7.1
odfpy            : None
openpyxl         : None
pandas_gbq       : None
pyarrow          : 0.17.1
pytables         : None
pytest           : 5.4.3
pyxlsb           : None
s3fs             : None
scipy            : 1.5.1
sqlalchemy       : None
tables           : 3.6.1
tabulate         : None
xarray           : None
xlrd             : None
xlwt             : None
xlsxwriter       : None
numba            : 0.50.1

</details>
