While trying to recreate this outside of my work code, I found that I cannot
do it in a simple manner- that is, just creating a ton of points and
plotting them doesn't reproduce the problem. I'm going to revisit this and
make sure it isn't a problem in my working program versus what I thought it
was, e.g. some sort of drawing limitation.
FYI, I get this using the Qt4Agg backend and am using MPL 1.0.1