Found the problem, sort of... It seems that GIFs written out with Paint Shop Pro 8 were somehow corrupt just enough to mess up the last line. I saved the exact same image with PSP 9 and the problem went away.
I suppose it COULD be something PF isn't handling right that it should, but I would think the blame would lie with imgdecmp.dll (or I guess the equivalent on the PC which I don't remember of the top of my head). But it's certainly possible it's a problem with PSP8.
In any case, since saving with a different version makes it go away it's not something I am personally worried about either way.