You can delete and re-add them..within 24hrs you will get refunded credits automatically. We do a PR check once a week (and will be doing it again in a few hours), and if your PR dropped, we will automatically move them, so no worries.
If you ever notice and don't feel like waiting for our in house PR update, you can always send in a trouble ticket and we will fix it right then.
Something worth noting for all sites (not just ours)...
PR is in a state of constant flux. At any given week we'll see 5 or 10 sites have a PR change. Sometimes it's even more. But wait a few days and the PR changes back. Google has different PR databases/servers just like they have different SERP and indexed servers.
When dealing with thousands of sites you see patterns that aren't always obvious with just a handful of sites.