liftgate opens by itself and generates "Trunklid OPEN" error

[SeattleTopaz]

This happens almost everyday in the morning. After the car's been sitting overnight in the garage when I pull out and the car is at an angle with the driveway I get a "Trunklid OPEN" msg on the dash at which point I have to get out, open and slam the liftgate closed again. Most of the time the gate appears to be securely closed, but I've had it be opened as well where you don't have to use the handle-switch to actually open the latch, it just lifts up.

Again, seems to occur only in the mornings or after the car has been sitting for a while so I suspect condesation is a culprit an I'm thinking the fault is somewhere in the switch for the liftgate that comes as that one-piece lift handle underneath the roundel. Any comments/suggestions from people who've experienced similar problems would be much appreciated... before I buy the whole part and have it painted.