Have you checked over at the Naturalpoint forums? I don't think the problem is in the game, or at least I am not experiencing it. There are many people using TIR here and I've not noticed reading about this being a common problem. I played a little and tried to 'mess up' TIR and wasn't able to. The only time I could cause something strange to happen, was if I moved back until I was nearly out of range of the camera. Then and only then would I get any sort of erratic behavior. Could it be you are too far from the camera?