This happens .It's happened to me and a bunch of others. WVI, I think, uses some control hits in there batches to catch people who are just doing bad work. I've had my qual drops to 80 and then be back to 95 in the same night before too.
New thead: http://mturkforum.com/showthread.php?33754-Can-t-Find-Tantalizing-HITs-9-8-It-s-a-Trap-Tuesday