incosistencies in dataframe.dtype.isin() - I am getting inconsistent with different runs on same code.
#### Code Sample, a copy-pastable example if possible

```
import numpy as np
import pandas

data = [[2, 'tom', 10], [3, 'nick', 15], [4, 'juli', 14]]

myDf = pandas.DataFrame(data, columns=['a','b','c'])

print (myDf.dtypes)

print((myDf.dtypes.isin(['int64'])))

```

#### Problem description

Problem is that I am getting inconsistent results based on running the same code:

So first run gives me:



```
a  False
b  False
c  False
```

and second (sometimes it takes up to 10 attempts) run gives me:

```
a  True
b  False
c  True
```

the second case is the truth and matches the myDf.dtypes:

```
a     int64
b    object
c     int64
```
.

Again to reiterate, I am not changing the code but when I keep running the same code I sometime get the first output and sometime get the second output. This is while I do not change the input, code or interpreter. I tried it on different machines and interpreters and still getting the same inconsistent result

the version of Python 3.7
the version of Pandas: 1.0



#### Expected Output

Consistent result (as it sometimes matches with the current output).

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

<details>

[paste the output of ``pd.show_versions()`` here below this line]
INSTALLED VERSIONS
------------------
commit           : None
python           : 3.7.4.final.0
python-bits      : 64
OS               : Darwin
OS-release       : 19.3.0
machine          : x86_64
processor        : i386
byteorder        : little
LC_ALL           : None
LANG             : None
LOCALE           : en_US.UTF-8

pandas           : 1.0.0
numpy            : 1.18.1
pytz             : 2019.3
dateutil         : 2.8.1
pip              : 19.0.3
setuptools       : 40.8.0
Cython           : None
pytest           : None
hypothesis       : None
sphinx           : None
blosc            : None
feather          : None
xlsxwriter       : None
lxml.etree       : None
html5lib         : None
pymysql          : None
psycopg2         : None
jinja2           : None
IPython          : None
pandas_datareader: None
bs4              : None
bottleneck       : None
fastparquet      : None
gcsfs            : None
lxml.etree       : None
matplotlib       : None
numexpr          : None
odfpy            : None
openpyxl         : None
pandas_gbq       : None
pyarrow          : None
pytables         : None
pytest           : None
pyxlsb           : None
s3fs             : None
scipy            : None
sqlalchemy       : None
tables           : None
tabulate         : None
xarray           : None
xlrd             : None
xlwt             : None
xlsxwriter       : None
numba            : None
</details>
