This morning, I logged into my Google Webmaster Central Sitemaps tool and noticed all my sites are "pending verification." I then found a thread at WebmasterWorld with an other person reporting this issue.
So I dug deeper and found a thread at Google Groups reporting this issue a while back, like a month ago. But Vanessa Fox from Google has a response that reads;
If your verification file or meta tag is still present on your site, try clicking the "pending" link on the My Sites page and then clicking the "Verify" button on the Verify page. We reverify periodically and generally this is done in the background -- we find the file or meta tag and the site remains verified. However, every so often, this reverification process is pending, and clicking the Verify button requests the reverification check right away.
If this doesn't work, please post back with your site URL so we can check into it.
My thoughts is that there was a bug, and when the verification ran, the bot couldn't find any of the pages it tried to verify. Thus putting the sites back into verify or pending verification status. I assume the next automatic run will resolve the issues automatically.
Forum discussion at WebmasterWorld.