SU-6 (AM-42) loadout bug

Would someone like to explain to me if this is correct?

Why it doesn’t allow me to load bombs if I have enough mass?

and Why it also doesn’t allow you to load a combination of bombs of 250/100 kg and 37mm cannons? neither in the wings nor in the bomb bay.

The other SU-6 (M-71F) allows you to use any bombs, why in this SU-6 (AM-42) has too many limitations on its loadout?