GMS Unleashed - bugs and problems

I noticed that Blackheart only disappears if I am on his right once he explodes into Mini Blackhearts. It's either that, or coming back and I am still on the right. I haven't once encountered a situation where I start on the left and end on the left where it ever turns invisible. I think I can recall once starting on the right and ending on the left that he did turn invisible. Try fighting entirely on the left.