I am unsure what features of my custom mission might have caused this, but here are the relevant parts:

1. An .sqf file that contains:
2. spawn {

_evac = createVehicle [heliType, getMarkerPos "heli", [], 0, "NONE"];
pilotType createUnit [getMarkerPos "heli", grpEvac, "thisPilot = this;", 0.6, "private"];
thisPilot moveInDriver _evac;

_evac setBehaviour "CARELESS"; //camera bug was present before this clause was added, I thought it had do
_evac lockDriver true;
_evac move getPos helipad;
}

Variables pilotType, heliType and others are declared in init.sqf

Then start scenario in multiplayer (I did LAN).
execute the .sqf, I did this with the debug-console in-game.
Go to the helicopter in spectator mode and left click it to track it.
The helicopter will start to rise and stop forward movement.
Stop tracking it to resume forward movement.

I am unsure what step caused this bug, but I suspect it is the spawn function, as the AI spawned in the thread might somehow interact with the spectator camera.

I as following the helo to make sure it was going to the destination correctly, then I saw that I could track the helo, so I did out of curiosity of this feature, but I did not correlate the tracking with the odd behavior for a few hours.

Arma 3 version 1.68.140908