Lccorp2 added some deths to take you over the river styx. This eventually started happening I have no idea. This happened to both the deths, suggesting to me that something got written where it shouldn't when the friendly wyrmling got summoned.
Just to clarify - what I did was to create a customblocker, then set the png to the sprite of the monster in question. That bug seems to happen with all monster sprites - just monsters. Ordinary animated .sprs seem to have no problem, the same with the newer monsters that come in .pngs.