Had the same problem - nowhere on internet found the solution - so i'm posting the solution:
This problem is caused by the lid that somehow triggers the Zoom multitouch function on touchpad.
If you don't use it (i don't) - just simply go to: Control Panel -> Mouse -> Multitouch Gestures (tab in mouse properties)
and uncheck "Enable Pinch Zoom"
This is the easy and working fix.
the other solution is to install some driver
(i don't know the details) from dell that disables touchpad when lid closed.
Posed there because google finds this page on the issue.