First of all I'm not sure all these hits really are 30mm hits.
Damage to my Ki was:
Aileron, flap, tail gun, engine, fuel leak so i took some damage (I however do believe that most was 20mm hits)
I think the "bug" consist of 2 things: First is the damage model, enough damage to a part and it fails and on bombers one 30mm might not be enough to destroy that part (seems like no damage) Second is that a hit on a control surface or flap can detach that part but the wing itself is intact so by hitting a lot of "small" parts a plane can absorb more damage than if the hits has been to the wing.