I've noticed some odd things happening when the Focus Distance Guide is on while re-framing the scene, most obviously affecting the camera Scale parameter. The camera controls operate on camera-aligned axes, and I suspect that Camera-Z is locked and Camera-Scale changed instead. I've also seen the location of the guide within the frame change. Are there things happening similar to the lens movements possible with some cameras, changing the view without the distortion arising from a camera tilt moving film and object plane out of parallel.