Sorry for the late reply (time zones and school). I believe it might have been the dark background thing (I have seen the yellow flashes occasionally) so I went through different coloured backgrounds and tried it out. Only a few times did I catch the a black flash instead of nothing (this was on brighter backgrounds) so I think you are mostly right. However (this may be just me or my copy of the demo), I am very sure I did catch a few times the core disappearing entirely when it was on two different backgrounds e.g. edge of a tree (if that makes any sense, hopefully that was helpful).
As a suggestion I recommend changing the black flash to a different dark colour as I found it quite jarring when I first saw it and I need to look closely to occasionally see the black flash.