On the F-15C, the desired heading marker is on the wrong side of the heading tape on the HUD when the bearing pointer points to the waypoint from the 6 to 9 o'clock position on the HSI. This bug has not been fixed for a very long while.
For the SU-25T, the keyboard command for "target size step decrease" (]) for the shkval does not work. Also the airspeed indicator on the HUD reads 10 kph when stationary on the ground.