I apologise if this has been reported before, however I did not see an Air combat thread list this bug.
I have just discovered a weird bug, if you intercept two UFO's within a close enough time and choose intercept on both rather than return to base on one two pop-ups. Once this occurs two UFO interceptor screens will appear and the control overlay of one will overwrite the others and they will share half the screen each where the interceptor is (though if you click on the plane the controls sorta switch, I managed to get the one being overwritten to attempt an escape). If you manage to kill a UFO the game returns to Geoscape but one interceptor screen will remain partially up (no controls) until you loose your interceptor (like I did) or luck out and it escapes or by some miracle your interceptor kills the UFO.
An odd bug that I can't imagine many people will have come across yet.