I don't have a good way to explain this just using words, so here's a partial screenshot:
Even when I set the threshold to 0, Fuzzy Select is grabbing a disproportionately large portion of an image. In the screenshot, I'm trying to only grab the darkest color. It's almost like there's an after-image stuck in the tool's settings. There's only one layer (with no layer mask) in the xcf, so it's not an issue of having the wrong layer selected.
Am I just flat-out doing something wrong? I tried messing with all of the other tool options, but haven't had luck.