Sometimes new users add redudent line break within header, which in wikitext looks like
== <br> HEADER ==
This line break is redundant as headers are displayed as block (not inline). Please trim <br> from headers.
(Not sure whether it should be handled in front-end of backend side or both)
I'm not sure but I saw different editors who use VE that does it, for example:
https://he.wikipedia.org/w/index.php?title=%D7%92%27%D7%99%D7%99%D7%9E%D7%A1_%D7%92._%D7%90%D7%A8%D7%AA%D7%95%D7%A8&type=revision&diff=17646264&oldid=17645521
Probably there is already a text of
<br> HEADER
and then the editor select it or part of it and transforms it to header, though I can't reproduce it.
This would be for the Parsoid HTML cleaner, but unless users are regularly creating these accidentally I'm inclined not to add it.