Tim,  Mine did the same thing for a long time after the door got slammed
(need to control my temper). The door would open frequently when I hit a pump
in the road or something.  After many unsuccessful attempts to adjust the
latch at the back of the slider door I finally replaced latch assembly-
problem solved.  Only after comparing the old and new latch did I recognize
that slamming the door was the fault.
Good luck!

Eric Small
South Portland, Maine
'86 GL Weekender  180K miles