Never been in that situation but I have been in a reverse situation.
I was doing a clubcheck, we finished the PFLs and other required elements so we were just fooling around a bit. I was doing a spin (I'm aeros qualified and current, and the aircraft is cleared for spinning) and found I had tremendous difficulty pulling out of the dive. Turned out the (non-aeros) instructor in the RHS had subconsciously gotten hold of the stick and held it tight. Fortunately I was stronger. Lesson for both of us.