After using some melee weapons, I think, the game will think you still have equipped a weapon and you won't be able to put any weapon or object in hands any more until you relog.

I droped the melee weapon but I wasn't being able to put anything in hands anyway.

I know the game thinks you still have something equipped in hands because while trying to use a fountain without anything on hands (I couldn't equip anything in hands anymore), the game told me "you can't fill metal pipe"