Thanks VirosaGITS and Dogie. I have tried power cycling both through the web interface and by turning the psu off and on. Same broken pattern, but oh well. Hashrate doesn't seem to be affected so I won't worry about it, it just seems weird and won't leave the back of my mind.

Now that I realize that row in the pool URL list is HW, I see that the percentage under DiffA lines up with that. It's all starting to make sense. Happily, it says 0.0000% so I'm happy about that.

Thanks again both of you for helping with what most would assume was very elementary, and making me feel welcome instead of stupid. Much appreciated.