Mine is an ATI, but the system settings aren't the problem. The drivers are just plain bugged, and I have had nothing but trouble with the graphics system from day one.
The first version would only kick in the GPU half the time. The second version would LOSE the ATI drivers entirely after a while, so I had to re-install it once a week or so.
Then a third driver set came out that mostly worked, but this full screen issue came up.
I thought about locking out the Intel chip via a BIOS setting... but Dell left that out of their BIOS.
So long story short - if I don't run in Windowed mode, I don't get high speed graphics.
I am never buying an Intel Switchable Graphics system again.