Dear Actipro support team,
I am not sure if this is the right way to contact Actipro Support, but my question is nearly the same as the question posted here, so I am trying to open the case again.
You may not have any reason to solve this, as it really can be solved by adding the status bar in the window's content. This is true in all but one case. If you use ResizeMode="CanResizeWithGrip" with the ribbon window, you are left with two, both unusable results.
The first one is to go with backstage not covering the status bar. The resize grip is then OK, fully working. But this is not usable, as the status bar has really to be covered by the backstage.
The second one is to put the status bar in the window's content, but then the resize grip will show as a part of unexistent status bar at the bottom of the window, so you get absolutely unusable UI (and, still the weird second status bar will not be covered by the backstage tab).
So, I found only one working solution, so far, that is to bind the IsApplicationMenuOpen property to both Window.ResizeMode and StatusBar.Visibility properties using custom value convertors, so the status bar will collapse and the resize mode will change appropriately to hide the grip, whenever the app menu is open. Yes, this works, but the window is slacking like hell whenever you click on the application menu (this is partly caused by MS and switching the ResizeMode at runtime, but still ...).
The conclusion is that this should really be fixed (or at least the styles should be adjusted appropriately; I really don't need to switch between 2007 and 2010 modes at runtime, so replacing the styles would work for me). I hope you will understand how this is important.