It's really weird. It's like you're getting a page that hasn't finished going through the vBulletin page mangle (hence the %1$s etc. tags).

Whilst I don't want to play the it's not my problem card, I've been testing with Google Chrome (for user cleanups) and I've not experienced any difficulties during my testing which has included logging out and back in again. Does your ISP have any monsterous caching proxy servers?

If you can clean your cache, just in case, and possibly try and establish if your ISPs are caching a lot.

Is anyone else having this issue?