his q sometimes doesn't work ( noticed it while fighting shaco ) happened couple times where he just get the scared icon above him but he continue attacking me !!
and a bug in his dance (not sure ) but he just freeze after couple spin in his dance 
I did see him freeze, but an enemy fiddlesticks made me walk away with his q so I'm not sure about that one.
The freezing is actually intended and was added back in patch 6.10. If you don't move for 5 seconds, Fiddlesticks freezes and becomes a scarecrow. I guess even if your dancing, your considered not moving.
