I am running same code and tried to reproduce this just by looping back internal sig generator.
Set to 200uSec auto trig 1/2 level full screen with circle button press. Triggers OK and screen updates properly when I change sig gen waveform, level and frequency.
This does sound weird to be a problem just on one specific setting. Someone a few posts back was saying something similar.
Maybe there was some bad images around at some point. Have you tried reloading the app and sys file?
Failing that you could post up the zips you are using for us to check out.