Silent failure on column reassignment
#### Code Sample, a copy-pastable example if possible

```python

In [1]: import pandas as pd

# Create example dataframe
In [2]: df = pd.DataFrame({'a':[1,2,3],'b':[4,5,8]})

In [3]: df
Out[3]:
   a  b
0  1  4
1  2  5
2  3  8

# Add 0 to end of series 
In [4]: df.a.append(pd.Series([0]), ignore_index=True)
Out[4]:
0    1
1    2
2    3
3    0
dtype: int64

# Add 0 to end of series and put replace in original dataframe
In [5]: df.a = df.a.append(pd.Series([0]), ignore_index=True)

# replacement fails without an error
In [6]: df
Out[6]:
   a  b
0  1  4
1  2  5
2  3  8
```
#### Problem description

The current failure is really annoying (as all silent failures are) because I have no idea A) why it doesn't work and B) how I can fix the issue.

What I expect: An error message saying something regarding why the operation did not succeed.

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

<details>

```python
In [7]: pd.show_versions()

INSTALLED VERSIONS
------------------
commit: None
python: 3.6.6.final.0
python-bits: 64
OS: Windows
OS-release: 10
machine: AMD64
processor: Intel64 Family 6 Model 60 Stepping 3, GenuineIntel
byteorder: little
LC_ALL: None
LANG: None
LOCALE: None.None

pandas: 0.24.2
pytest: 3.6.4
pip: 19.0.3
setuptools: 39.2.0
Cython: 0.28.4
numpy: 1.13.3
scipy: 1.1.0
pyarrow: None
xarray: 0.11.3
IPython: 6.5.0
sphinx: None
patsy: None
dateutil: 2.7.3
pytz: 2018.5
blosc: None
bottleneck: 1.2.1
tables: None
numexpr: None
feather: None
matplotlib: 2.0.2
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml.etree: 4.2.3
bs4: None
html5lib: 1.0.1
sqlalchemy: None
pymysql: None
psycopg2: None
jinja2: 2.10
s3fs: None
fastparquet: None
pandas_gbq: None
pandas_datareader: None
gcsfs: None
```

</details>

#### So why are you even trying to do this anyways...?
Basically I want to verify that a part of my code is working right. The easiest way to do that is to simply replace the output data that exists with a simpler form. In this case, I add an extra data point to the independent variable series and then use that as an input on a function:

```python
df.a = # Add a zero point
df.b = df.a*5 #or some other really simple function like that
```
