For hard to shut rear hatches, or those that pop open while driving (particularly while cornering), use a torx socket to loosen the two bolts that hold the latch bar to the chassis. Slide the bar (shaped like a U) towards the rear of the car. Re-tighten. I had to move mine out about two or three millimeters, now it's a perfect shut every time, and hasn't popped open in the corners since the fix.
The sockets are cheap, and certainly better than griping to the dealer about a niggling problem which seems to be forgotten during the service checks.
Cheers,
John
