I contacted dell support after reading this thread.
I gave them them link to the thread as well, og they wantd my xps in for repair, so gonna be intresting what they find out.
It seems to be that the windows button is one way the device is woken from sleep mode. I noticed if I put the tablet to sleep and close the tablet to the dock the display will come on before the tablet is touching the dock. It seems to me that when closing the dock hinge is putting enough pressure on the windows button (which is covered by the hinge) to wake the tablet. If true, since modifying the hinge seems unlikely, we would need a way to disable the windows button from being able to wake a sleeping tablet.