Here is what I am finding with the mid-February 1.3.3.13svn snapshot, on a WinXP machine:
When grabbing the handles at the middle of the frame edges (ie, not the corners), Alt alone, Shift+Alt, Ctrl+Alt all behave the same. The frame resizes and the contents are rescaled in the direction you move the handle. When grabbing a corner handle, Alt will allow enlargement/shrinking without constraint (ie, this can be non-proportional). With both Ctrl+Alt and Shift+Alt, enlargement/shrinking of frame and contents only occurs in a proportional way. I will next check to see what happens in 1.3.5svn. Both
