My 08 started doing this today. Only difference I noticed was squeaking sound as it closed earlier in the day. Then when I got home it started doing the almost closing then opening back up. Only way I got it to close was stop it as reopened it would slam shut.
So did you get this fixed or are you still trying to figure it out?
My 07 randomly opens itself and after "fixing" that problem by disabling the rear access I can now only open the gate with the key fob. Liftgate handle doesn't work..... Before, you'd hear the latch actuator when you pulled the liftgate handle, now there's nothing and the gate won't open manually.