BUG: Bug in DataFrame.loc for setitem changed dtype when setting more than one column
- [x] closes #18415
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

Could not find a reason why we should convert the dtype to object, if values is already an array.
Hello @phofl! Thanks for updating this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:







There are currently no PEP 8 issues detected in this Pull Request. Cheers! :beers: 

##### Comment last updated at 2020-12-23 23:51:05 UTC Done cc @jreback  Merged master This pull request is stale because it has been open for thirty days with no activity. Please update or respond to this comment if you're still interested in working on this. This pull request is stale because it has been open for thirty days with no activity. Please update or respond to this comment if you're still interested in working on this. @phofl can you merge master to resolve conflicts @phofl status on this one? @phofl closing as stale. reopen when ready