Ran into a fun problem leading me to immediately think the worst, that something was corrupted with my software somewhere.
I was hearing two wrong things:
Long story short, I think it was the fact that my piano had two (internal) voices turned on and apparently this was somehow getting translated into a double-strike on the piano.
But what's odd is that I can't tell from the piano roll that anything's wrong. I see no double notes, yet playing the bad parts back would produce identical results.
Some days I really hate computers.