I posted two video at Dropbox -
https://www.dropbox.com/sh/8o4zv8wna51ud6s/yN4xq7nKNZOne shows no stacking when the cursor is moved straight to the right. The other shows stacking when the cursor is moved right and down. This stacking does not occur using Firefox and also does not occur when I use IE9 on a very (27 in) wide monitor. The problem is occurring on a 19" monitor and a 15" laptop.
I have been playing with what is in the cell to the right of the menu cell, and it seems that if there is something (text or image) close to the left edge of the cell to the right of the menu cell, it wont stack, but on this Mission Statement and Goals page, there is nothing close to the left edge, and stacking occurs.
I checked Easy Button & Menu looking for something to control the persistence of the submenu but did not find anything. Perhaps, since the submenu pops out, then stacks, some persistence might solve the problem.