Lines starting with a hash without spaces before the words stopped to be recognised as headers [duplicate]

Question

I made a small edit of the post https://stackoverflow.com/revisions/25855713/5 that showed steps and sub steps as html headers, and noticed that after my change the steps start to be shown as plain text, e.g. #Step 1 - Understanding Basic Authentication.

I decided that it was caused by my changes and reverted to previous revision 4 created in 2016. Unfortunately the formatting wasn’t restored.

I am guessing that since 2016 Stackexchange replaced its markdown interpreter and stopped recognise # without spaces before text as headers. In the markdown documentation https://daringfireball.net/projects/markdown/syntax#header space after hashes is shown, but not documented and some implementations enforce space, but other do not enforce.

I believe that old html was cached and showed headers correctly before I touched the post.

If my explanation is correct, it will be good to run convertion to update all old posts:
For lines starting with 1-6 hashes without spaces before the text to insert single space after the hashes to make backward compatible support of hash headers.

Answer 1

I don't see the value in doing this.

There are less then 4% of all posts that didn't get updated with the Commonmark migration:

With the auto-fixing utility we estimate that we’re going to land at over 96% of all network posts being rendered completely identical after migrating to CommonMark and using the new renderers.

_{From here.}

Of that 4% only a fraction will ever be edited again, in those cases users can easily fix the headers themselves. If they don't do that someone else will notice, as the edit bumps the post to the frontpage.