High Nightmare,

I don't have such problems (I have others :-) ).
Sounds like a problem with your graphic card, because as you wrote, sometimes it works, sometimes not. What graphic card do you use? Tried it on different PCs? If you don't have any, I can test it for you on about 5 different PCs with different graphic cards if you post a link somewhere.
Have you installed latest drivers?
Maybe you have configured some settings in display-settings-advanced that cause this behaviour?

Just some ideas....

Greetings,
Dirk