I sometimes appear to be logged into some other user's account

it happens when reloading a page or navigating back. it shows me a different user's account in the top bar -- worried that if someone hits stop during page load, they'd actually be able to impersonate another user's account. this appears to be random and I've seen several different accounts over the course of the day.

sorry if this is an already known bug or if it's just a cosmetic issue that doesn't actually give anyone perms.