Vessels can be hijacked from spectate mode if you EVA and board before a protovessel update

[godarklight]

As per description... Solution will be to kill spectator kerbals or somehow remove the ability to EVA.

[Xinayder]

I think I've managed to fix this. Add the ControlTypes.ALLBUTCAMERA control type to BLOCK_ALL_CONTROLS on VesselWorker. That way, the kerbals wont even show.