Hi all - yep, this is a known glitch, previously discussed in another thread or two. I can guarantee you that engineering is all over this one - and I'll post again when I have a substantive update.
Fortunately, this has affected only portions of an account, for a very tiny percentage of AdWords advertisers. With that said, I know that this fact certainly doesn't help if your account is amongst the few that are affected.
And, if your account has been affected, please accept our apologies.
BTW, I've now talked with one advertiser with the issue - and we found that rebooting her computer, and then logging in from a non-bookmarked page solved the issue for her. I'd guess that this will not work in every case, but it's well worth a try at any rate.