Well it is complicated. My guess is the problem is because you align +Z and +Y of the camera to Cpivot and then go on to align +Z of Campiv (which the camera is parented to) to Tpivot. I think this gives the X axis a bit too much freedom and hence the roll. (If you use mouse inputs for turning you can make the roll wind and unwind by moving the mouse in clockwise or anticlockwise circles). In any event there is a conflict there that you need to resolve.
BTW. Turnentity might suck, but at least it avoids gimbal lock. Maybe it slerps.
BTW. Turnentity might suck, but at least it avoids gimbal lock. Maybe it slerps.