Occasional rendering artifacts

Reported in ggez here, but couldn't reproduce it until recently. Sometimes there are small rendering artifacts in text, such as at the top of the P and Y here:

Or the bottom-left of the A here:

I thought this was something platform dependent rather than a flaw in ggez's rendering, since I couldn't reproduce it on the my systems. However, when dealing with another text issue here I noticed artifacts that reminded me of the other issue, particularly the right edge of the 5 and the left edge of the 4 here:

And this time I COULD produce them on my system, looking at the 2, the 9 and the 7's:

So, I'm not sure where to go next with this. Is it a flaw in the font? In rusttype's interpretation of the font? Or in ggez's rendering of what rusttype gives it?