Hmm.. I have no idea what that spike could possibly be. I don't even know how I would figure it out. I tried adjusting the sliders so it surrounded the one spike, but there was nothing obvious in the display. Just looked like a blank screen.
The same spike actually exists in all my subs. Here is #0013 which was able to successfully tell me the number of stars from the image history window. The same spike can be seen in the histogram.
https://dl.dropboxusercontent.com/u/54413223/Sh2-129_LPS_1200sec_0013_-10.2C.fit
Any idea why one of them works and the other one does not?