Pretty sure you're thinking of Entropy/Darkness that uses Dolls and Pandemonium.
Not a bug. When a Doll is frozen (in this case by Pandemonium), it freezes the opponent's weapon.
(extra tip: you can Shockwave the owner of a frozen weapon to destroy that weapon. it even works for protected weapons, including Morning Star, and it's the only thing that can destroy protected weapons. other protected perms can't be frozen as of yet.)
