Unused menu entries

You probably are seeing a bug in MediaWiki where the sidebar occasionally reverts to default settings.

Could be. It is not occasional for me though, it is consistent when I use 'en' as interface language.

Has the bug been reported?

You're right, I see it as well, and it's indeed using the default sidebar for some reason. When did it start doing so for you?

I have no idea when it started doing so, but I think it has been like that for a while.