1. Open up Stratis in the editor.

2.Place a helicopter anywhere on the ground and give it a few move way points.
3.Next place a single rifle man somewhere, right click the soldier and select "play as the character".
4.Once in the mission hit ESC to bring open the menu and select "spectator" from the debug consol.
5.While in spectate push "M" to open the map, while on the map left click on a location from which you can observe the helicopter moving. Notice how the helicopter is following it's way points correctly.

Now to replicate the bug,
6.On the left side of the screen you'll see a list with the rifleman player character and the two AI helicopter crewmen. left click on the name of one of the crew to select them.

7. Observe how the helicopter stops following it's waypoints. It'll come to a stop, pitch the nose up and begin to climb for as long as it is selected. It may also start to slowly move backwards.
8. Left click on an empty area within the field of view to deselect the crew member. Within a second or two you notice the helicopter will resume it's way point course.
9. If you select a crew from the list on the left again or directly click on the helicopter to select it, it's AI will break again and begin to climb.

This happens with all helicopters. I've run a similar test in which there were two helicopters not grouped together, and it seems that if you select one helicopter both would stop and start climbing non stop until deselected.