Thread:Project:Support desk/Deleting "Category:Pages with broken file links" *and* removing erroneously-created not-actually-existing categories/reply (2)

For the MediaWiki:Broken-file-category thing - replacing with a single hyphen will only take affect after the next time pages in that category are edited (Or unless you run refreshLinks.php which could take a while on anything other than a small wiki).

As for most linked categories - this was a regression introduced back in 2011 (r103759) as part of trying to make the query more efficient so it can run quickly on big wikis. It was recently fixed last month (bug 58967; fix is currently scheduled to be included in 1.23 whenever 1.23 gets released). If its really bothering you, you could try to modify includes/specials/SpecialMostlinkedcategories.php to add the fix (Its a one line change adding  after line 46. Normally we recommend never to do custom modifications to mediawiki files, but this change is going to be in the next version anyhow).