Part of the problem is that super-8 projectors were typically 18fps (I think), so the screen flickers 18 times a second and your camera records 25fps, meaning that you'll record a flicker on the camera as a result. It's not the auto exposure, because that typically takes at least a second to decide to change, but the varying light levels on each camcorder frame. You may be able to adjust the projector speed to 25fps, but unless it has some kind of crystal sync then it will wander anyway so you'll still get some flickering.