In these cases, you can try to make a "null edit" to MediaWiki:Sidebar. That usually resolved the issue. The origin is unknown.
That page is protected for me, wouldn't it be for him as well?
Probably. I'll make a null edit. Let's hope that works.
Thank you. Now I have the correct sidebar again.
Similar also happens to me every now and then, when I suddenly see the MediaWiki default sidebar with Community portal and Current events. Is there already a bug on this?
There once was an issue in bugzilla that addressed this, but as there is no way to consistently reproduce this issue, the issue was closed, IIRC (rightly so).
