It just came to my attention that we're getting them. Researching it, it's a bug in MediaWiki itself and it surfaces when you move massive amounts of pages at once. The bug report on MediaWiki's site says 3 out of 7 move queries generate it - and Zegridathes reported that he's attempting 30 tabs at once.
There's nothing I can do about it right now, so it seems, and it's no indication of poor server performance or database failure for MyMMOWiki. It'll chill out once the bulk of the pages get moved or MediaWiki releases a patch.
I've mitigated it as best I can by installing a memory cache daemon - but they'll end when there isn't mass-moving of pages or there's a patch released. If they don't, we know it's something else lol - but their description fit our situation so it seems that's what it was.