You're not alone. Something seems to have gone wrong with the way hidden purchases are handled at the moment. There have been some repairs already as earlier confirmation prompts weren't being shown when things were hidden, and it wasn't possible to get to the hidden purchases management page in the account area. Those are fixed, but I'm still seeing what should be hidden content in iTunes, iOS and Apple TV, and if I attempt to hide anything it pops back after a second or two.
It isn't clear how widespread this problem is, but use Feedback - iTunes - Apple to let Apple know this is affecting you too.