I can't understand why the Picture Editor mask button isn't working for you.
Here's an example of it working.
This is the image displayed in the editor:
<img src="http://img62.imageshack.us/img62/3875/18850755.jpg">
And this is the image displayed in the mask editor after I'd erased parts of it for comparison's sake (notice the red line around the display area):
<img src="http://img519.imageshack.us/img519/4774/73317056.jpg">
Clicking the mask button toggles between the 2 displays.
I'm using 99.82, so maybe it was broken in 99.62?
Krush.