BUG: Fix unwanted type casting while replacing values in a DataFrame
- [x] closes #32988
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

As mentioned in #32988 [here](https://github.com/pandas-dev/pandas/issues/32988#issuecomment-604727057) I think, that I have found a way to fix this, but I don't know, if this results in a desired behavior. 

I would add tests after ensuring, that this does not break anything else. 

Any thoughts about this?
Thank, I'll follow this way in the future. 

I added a test.

When you use a value, which is actually replaced in the test, the pd.NA is converted to np.nan, if the original DataFrame had float64 as datatype. The example given in the issue did not replace a value from the original DataFrame.

Don't know, if this is a desired behavior. i've labelled this as a regression, see https://github.com/pandas-dev/pandas/issues/32988#issuecomment-605519281 cc @jbrockmendel  can you merge master and see if you can simplify Thanks @phofl for looking into this. #32988 has been addressed via #34048.