After you've opened a stack, and you double click the home button to go to your favorites, the stack is still visible and the dock is still "there" but invisible.
I can still open and close the stack by tapping the area where the stack icon is supposed to be, and open Safari by tapping the area next to that, as if the dock is still there. This can be fixed by going back to the home screen and closing the stack, but I just thought you'd like to know.
Also, sometimes the iPhone freezes in a position where the whole screen is blacked out, as if a stack is open, but it's not.