Rpg Maker Developers Group

I've found a very annoying visual bug with JM's Earthbound Battle Backgrounds, and I have absolutely no idea how to fix it.
Here's the plugin in question.
This plugin's supposed to cycle through a color palette on grayscale backgrounds, but I've discovered a flaw in it.

Basically, the palette shift is being overridden somehow, with colors being skipped or outright replaced. (The bright colors have been placed there to demonstrate the problem.
This plugin operates on grayscale patterns, like this for example, with the colors supposed to be cycling through from left to right on the plugin bitmap. The white color starts the first in the line, the next darkest one is the next one, and it continues like that. Black is transparent.


But for some reason, colors #FFFFFF (the lightest) and #111111 (the darkest) are rendered as the same color, even though they're clearly different in the palette.
I'm at my wit's end on this one- if anyone can figure this out, I'd love to hear any possible solution, since I've put a ton of work into using this plugin already and i REALLY don't want to have to throw it out.


UPDATE: I've tested it in a new project, and with multiple palettes and patterns. It still happens regardless.

UPDATE 2: I've figured out how precisely the bug works- it starts off with everything being totally fine for one frame, then it breaks immediately after with #FFFFFF being overridden by the color that's being displayed in #111111.
Doesn't help me fix it, but if the plugin author or anyone more skilled in coding than me feels like taking a look...