Word to those who are having this problem:
If you are using Opaque Menubar to turn your translucent menubar into a solid color, you might experience a problem with the desktop background.
If you set a desktop background that is not *exactly* the same size as the screen, it will be immediately scaled to fit the screen. Trying to tile? Won’t work, it will rescale the single tile to fit the whole screen. Etc.
I’ve had this problem for a week before I got tired of it and dug in to fix it.
Turns out that the OpaqueMenubar does some fancy trickery with setting the desktop background in a certain way to turn the menubar a solid color. The unfortunate side effect is that is causes this background scale-to-screen problem. Killing the Opaque Menubar process reverts the desktop background to whatever scale/tiling/centering you want.
It’s a bit frustrating, because I do like the solid menubar, but I like a nice tiled background more.
Note: this bug also causes any sort of dynamic background (like the very awesome EarthDesk) to revert to a default (and static) Mac background image.