I discovered this happens when cleaning the display. When I apply pressure to the lower right end under the hinge, the screen turns off.
The pressure has to be quite high but obviously not high enough to damage it.
This video explains it:
(Please visit the site to view this video)
I'd appreciate if anyone could check his/her laptop for the same issue and reply to this thread.
Also, if a Dell Support representative could show this to their technicians and report back, that would be great.