When moving between F and C on the weather app,
the max/min temp can leave a few stray pixels.
I did just replace the screen, but it is fine on all other
pages, so I think this is a bug.
Correction, there is some image persistence associated
with this new screen; I have a second screen (different model)
on the way, but it will take time.
A few days in place, and the problems seem to have disappeared.