When pressing the trim button in the hind the stick position gets locked in a slightly more pitch up (pulled towards) position than it was held when the button was pressed. this results in the helicopter nosing up when ever you trim.
you can see this when not moving the stick and pressing the trim button the stick will trim slightly towards you when pressed.
Edit: made a track file of the issue, did a hotstart on ramp and air start. Trim issue seems to only be there when AP Pitch and Roll is enabled.
Hind Trim Issue.trk