A locked air target cannot be undesignated.
Lock and track air target in either RWS or TWS and/or STT
Bug will not undesignate, HUD symbology maintains tracked target, radar keeps target bugged.
You can select next target but not undesignate them, only cycle through.
You have to manually move bug to new air space outside of scan to undesignate or move aircraft outside of gimbal limit of the radar.
Tested in Stable and targets can be undesignated.
No mods installed and using the same joystick profiles on both OB and Stable.