Okay. So, official news is: We had of a bit of an issue where we got compromised in an non-delightful manner.
That's been resolved, and while we were at it, we did a much needed upgrade to the forum software as well.
I can't say for certain whether or not the current condition of the nav bars was a result of the compromise or the upgrade, but it seems to be purely CSS cosmetic related and should hopefully be sorted out soon enough. I put a NEWS notice up regarding it, but at the moment, no ETA that I can give as I don't normally deal with that.
I feel bad leaving it for Sandwich to deal with, but the clean up and getting the forums back online (in addition to tracking out how it happened in the first place) took WAY too long as it was.