BUG: fillna ignoring axis=1 parameter. #17399
- [x] closes #17399
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17409?src=pr&el=h1) Report
> Merging [#17409](https://codecov.io/gh/pandas-dev/pandas/pull/17409?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/fe66b5622e35a51cdc4fa1fbcada0404fb3acc9b?src=pr&el=desc) will **decrease** coverage by `0.28%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/17409/graphs/tree.svg?src=pr&width=650&token=eZ4WkYLtcO&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/17409?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #17409      +/-   ##
==========================================
- Coverage   91.53%   91.24%   -0.29%     
==========================================
  Files         148      163      +15     
  Lines       48777    50097    +1320     
==========================================
+ Hits        44648    45713    +1065     
- Misses       4129     4384     +255
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.05% <100%> (-0.85%)` | :arrow_down: |
| #single | `40.24% <57.14%> (-1.36%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/17409?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/generic.py](https://codecov.io/gh/pandas-dev/pandas/pull/17409/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ2VuZXJpYy5weQ==) | `92.44% <100%> (-3.47%)` | :arrow_down: |
| [pandas/tseries/converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/17409/diff?src=pr&el=tree#diff-cGFuZGFzL3RzZXJpZXMvY29udmVydGVyLnB5) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/core/computation/expressions.py](https://codecov.io/gh/pandas-dev/pandas/pull/17409/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29tcHV0YXRpb24vZXhwcmVzc2lvbnMucHk=) | `0% <0%> (-93.28%)` | :arrow_down: |
| [pandas/io/msgpack/\_version.py](https://codecov.io/gh/pandas-dev/pandas/pull/17409/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL21zZ3BhY2svX3ZlcnNpb24ucHk=) | `44.65% <0%> (-55.35%)` | :arrow_down: |
| [pandas/io/clipboard/clipboards.py](https://codecov.io/gh/pandas-dev/pandas/pull/17409/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2NsaXBib2FyZC9jbGlwYm9hcmRzLnB5) | `26.58% <0%> (-5.61%)` | :arrow_down: |
| [pandas/io/parquet.py](https://codecov.io/gh/pandas-dev/pandas/pull/17409/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3BhcnF1ZXQucHk=) | `65.38% <0%> (-4.52%)` | :arrow_down: |
| [pandas/io/json/table\_schema.py](https://codecov.io/gh/pandas-dev/pandas/pull/17409/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2pzb24vdGFibGVfc2NoZW1hLnB5) | `95.83% <0%> (-2.37%)` | :arrow_down: |
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/17409/diff?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `65.2% <0%> (-1.76%)` | :arrow_down: |
| [pandas/core/common.py](https://codecov.io/gh/pandas-dev/pandas/pull/17409/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29tbW9uLnB5) | `91.18% <0%> (-1.74%)` | :arrow_down: |
| ... and [95 more](https://codecov.io/gh/pandas-dev/pandas/pull/17409/diff?src=pr&el=tree-more) | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17409?src=pr&el=continue).
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> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17409?src=pr&el=footer). Last update [fe66b56...e09189e](https://codecov.io/gh/pandas-dev/pandas/pull/17409?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 @TomAugspurger -- added and updated the changes. can you rebase / update can you rebase and move the note to 0.21.1 can you rebase / update Moved `axis` work to internals, setting axis for `mask.cumsum()` seems to do it.
   @pratapvardhan can you rebase and update to comments closing. would like to have these fixes. pls ping to reopen and fixup. Is this possibly still an issue?  I'm able to reproduce it, but with 0.24.2 which should long-since have the fix:

https://imgur.com/a/3ZrXqSv @jorvis the issue is still open if you want to try to pick up here

this PR was never merged as it had gone stale  Sounds fun, as long as you're OK being patient with my learning here.  I added a comment after your review in his PR, since the change you were asking for wasn't clear to me.