Live Blank Screen button works fine when nothing has gone Live. After showing ie a picture then the Blank Screen button has no effect.
The latest revision, 749, should fix this.
morgan, please join us in IRC and post on the tester mailing list. A lot of these issues we do already know about, and might have even fixed already. If you find a "bug", just pop into IRC quickly, and ask the guys in there if they know about it.