Torsion Spring Installation - Winding Unit Problem

I'm installing a 16x7 garage door with an EZ Set torsion spring system. I'm just about done but when I begin to wind the spring, after several turns, the winding unit starts to slip out of its seat in the bracket. I immediately stopped because I'm afraid of what could happen if it gets free. I managed to unwind the spring without completely loosing it, but I have not been able to get it fully wound without slippage. Anyone run into the this problem before? Or is it even a problem? Seems like the weight of the door will hold the thing in place, but I'd rather be safe than sorry. Any tips would be appreciated.

 

Please post picture of each end of the tube/drum assembly and are you winding it the correct direction?