When I start a mission without a preset loadout and let the groundcrew mount bombs on the Mossie, it is currently impossible to drop the wing mounted pair of bombs.
They could neither be dropped or jettisoned. (The bombs in the bomb bay work fine.)
If I do the same with a preset loadout, everything works fine - so it's (maybe) not me.
Where: Single player - custom mission from mission builder
(I guess it is possibly the same issue like in Multiplayer with the wing mounted bombs.)