Garrrrhhh... you're right! When I ran the tests in post #438 I had not sudo'd to root on the device running the stock xserver - when I sudo to root on the device with the stock xserver, the blanking is reproducible.

I really don't think this is an issue that warrants further investigation unless you can fix it without spending much time on it - under normal circumstances users shouldn't be running apps as root, and other than when I'm testing I would typically use the GUI anyway.