I see deer as being just very finicky and on edge. I think that a single deer at any given moment will or wont be spooked by the flash and or the sound of the camera. I have does standing around "posing" for the camera one day and then have them in blur mode in mid stride the next. I also just got pics(which I posted) of a mature(consensus shows, since he's at least 3.5) buck that walked into the frame and then stopped in the next frame, unspooked. I think the deers' individual personality has a lot to do with it too.