blaze will not drop anything unless killed by a player. I tested this on a craftbukkit-1.5.2-R0.2-20130604.210404-10 server with no other plugins running at all. Recently Upgraded to craftbukkit-1.6.2-R0.2-20130814.074349-13 Server issue still exists. I tested blaze being killed by suffocation, water damage, and potion/arrows shot out of a dispenser. I tested making skeletons drop diamonds and zombies as well they drop configured drops through fall damage, suffocation, potions/arrows shot out of dispenser so it seems to be blaze specifically.