Hey, tpiom, that's basically what I just did about 30 mins before seeing your reply on here, weirdly enough, after a full re-install, I loaded up K2, used the command keys to activate the free-camera and it started doing it again! But I seemed to be able to change the direction it was moving by pressing the directional control keys for it, very weird. But then, say if it was tilting left, I hit the key once for tilt left, it stopped! And it hasn't come back since on either K1 or 2, really weird.
I think it's to do with the shift key, not only is it the modifier for the speed of the camera, but holding it whilst holding down the tilt buttons seems to lock it in that direction, and only tapping said key again on its own without shift seems to stop that, too. I'm just gonna put it down to me being clumsy with what keys I'm pressing. Panic over!