That's called code-share, it is up to the airline/airport to decide if they want to show all the flight numbers on the screens. If you display all flights it takes an age to get back to the operating (BD) flight , if you don't then you have customers staring in confusion at the screens looking for which desks to check-in at. Your are damned if you do and you are damned if you dont, This problem is not unique to bmi.