Hoya filters are noted for having such problems. Personally, I've seen three such problems with Hoya filters due to the retaining ring not being properly seated or coming lose. Granted, it's not a common occurrence, butit happens.My experience mirrors this. I'm not buying any more Hoyas.
Same reason I buy B+W and Heliopan filters. It's a relatively rare occurrence but a pain when you get a defective.
Godfrey
