BUG: pd.concat produces frames with inconsistent order when concating the ones with categorical indices
- [ ] closes #44099 
- [x] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [x] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [x] Added an entry in the latest `doc/source/whatsnew/v1.5.0.rst` file if fixing a bug or adding a new feature.

Hello @tyuyoshi! 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 2022-03-25 07:30:01 UTC > can you add the example from the original OP as well and put a test in pandas/tests/reshape/test_concat.py

Thanks! I added the test case in this commit(https://github.com/pandas-dev/pandas/pull/46019/commits/a66a60fe6284b7380303d514cacfac14f29693d8) This pull request is stale because it has been open for thirty days with no activity. Please [update](https://pandas.pydata.org/pandas-docs/stable/development/contributing.html#updating-your-pull-request) and respond to this comment if you're still interested in working on this. Thanks for the pull request, but it appears to be stale. If interested in continuing, please merge in the main branch, address the review, and we can reopen.