This is a pretty funny glitch that happened while I was trying to add boss introduction title cards to The Legend Of Doodle (http://thelegendofdoodle.com/). I figured I've been sitting on it for long enough, so here you go!
It's happening because the global flag about whether the boss is currently happening was moved to take place after the title card disappears - so that the HP meter doesn't show up beforehand - but this boss in particular relied on that value to stop him from spawning. (I think, anyway, or something similar. It has been several months since I've looked at that code, or even thought about it.)