When in the tank cannon sight position, if you move your head, the view sweeps across the terrain in a way that is nauseating.
This same effect occurs when you use the same button I would use to turn off trackir to set a head position.
I think the bug is there is no way to fully turn off the VR camera like there is to hold your head position fixed like when using trackir in AH.
This same effect happens in the 17 pound'er.
This problem also complicates setting VR head positions in planes and GVs.