I once had an issue with a 350B2 that could have been a disaster had altitude not been on my side. At about 2000ft, the hydraulics were isolated on the central collective (after simulating a slider valve seizure) and the student started to slow down too much. As airspeed decayed, he began to lose control in yaw (to the left) so I quickly said "I have control" and started a recovery. As I applied a significant amount of pressure to the right pedal to correct the yaw, my seat slipped back on the rail and I could no longer get enough movement on the yaw pedal to regain control. After a few tense revolutions where I unsuccessfully tried to dive on airspeed to get control back, I shouted at the student to switch the hydraulics back on. (There's only one switch on the standard 350 and it's on the central collective).
I wonder if the seat slipping on the rail could have contributed to this crash?