When Rhino-Hunting, the driver (spy) will get the same rank as does the gunner (tank).
After zoning, sometimes the rank of one of the teammembers will reset.

Personal fix:
Get out of the rhino, get in again, OR
Open skillwindow and press ANY plus-button (rank will update). Press again, rank will be down, press again, rank will be up.


Also, if the rank of the driver (spy) will be up, he does not get XP / money when the gunner (tank) will get out of the rhino and use another weapon (near equal ranks, one is 2 ranks lower). Teammembers are in range of each other.