Did the Japanese aircraft bombs use "Shimose" (picric acid) like their artillery shells and handgrenades? It was highly reactive with steel projectile casings (especially in tropical environments), producing very sensitive crystals.
My aunt's boyfriend was in the Army in New Guinea and said that it was common to find boxes of Japanese grenades which had disintegrated, leaving the grenades scattered on the floors of the huts where they were found. It was SOP to throw a very long loop of rope to the far side of the grenades, instead of initially picking them up by hand. That way, if they went off by themselves while being dragged across the floor, you had some distance between you and them.
I can't imagine that 250lb and 500lb bombs full of the same stuff would be much more fun to deal with, by the Japanese OR us.
Update: I see that at least some of them were filled with Shimose. Nasty stuff.