I've got a number of animations and I am continually finding and fixing the same problem: my lights change settings over the course of the animation.  When I created the scene I locked all of the lights.  The first time the settings changed, I created a single frame light-set from the first frame to apply to the end frame.  For some reason, it changes the lights on the first frame also, and so I apply it there as well.  When I then scrub the animation it looks fine.  But whenever I load an animation to create a new one from it, the lights will often do it again, seemingly randomly (but always the same changes).  I have a number of clips, and the frequency with which I am seeing this happen goes way beyond what I would expect if it were a simple oversight with just one clip.  It really seems like any of my clips may just suddenly revert back to this behavior, and I can't figure it out.