the back hatch glass pops open sometimes on it's own

2003 chevy blazer 4dr.when I open the driver side door the back hatch glass pops open,sometimes.The button on the dash will not open the hatch.The button on the hatch itself will not open it either.I tested and I have 12v on all wire plug hook-ups in the back hatch. When I unplug and replug up the actuator,it will pull in but will not stay in.Not sure if this is the way it works or not. Could there be a problem with-in the actuator its self?thanks