Same problems. This is what I did to fix it.
1-21-2013 Projecting pictures with Macbook Pro with OS X 10.8.2 (Mountain Lion), and Epson EMP-83 projector connected via the mini display port.
When the Epson EMP-83 is connected to the mini port on the Macbook Pro, the display may need to be changed. Go to System Preferences, Display. Press Option key, and notice the "Gather Windows" button changes to "Detect Displays". Press Detect Displays.
The Epson PJ profile comes up behind the present window. Select the Arrangement tab, and make sure that the "Mirror Displays" box is checked. You will see two windows which become superimposed when the Mirror Displays is checked. "Mirror Displays" in this case means that the two will be the same
If you should leave it unchecked, the two display icons will be in some arrangement. Press the Option key, and drag one icon to the center of the other one. This would allow you to have different screen resolutions.
I found that the mouse disappeared if Mirror Displays was unchecked. It turned up to be about a mile to the left, well off-screen. Repeated swipes brought it back to the main display.
Hope this helps.