For what it's worth, WordPress MU Domain Mapping plugin v 0.5.1 is not fully compatible with TinyMCE Advanced plugin v 3.2.7
In TinyMCE Advance, the bug is when you click on a table icon or other icon that brings up a popup. Then the popup is blank so you can't use it to make tables for example. Deactivate the WordPress MU Domain Plugin and the issue goes away.
If I deactivate the plugin for an individual site, the mapped domain still works as long as I keep it activated for the main administrative site.