I have also detected this problem, and this one which is nearly the same : "Hide the Document Tree, Toggle Full Screen ’On’, Show the Document Tree..." Now EditArea is too large But no time this week to search for a solution...
Sorry no progress on RC3 ...Turns out I found another bug with Full Screen/MODx manager...
To replicate: (Ensure the Document Tree is ’visible’), Toggle Full Screen ’On’, then Hide the Document Tree...
I agree, that would be nice. We will add this suggestion in the Todo list...
also could you like add a loading or working sign when editarea is loading