Not all mobspawners drop mobheads, but I noticed that chicken spawners DO. Is there a way to disable it for all mobs?

Strange I dont check the mob type at all.

PS. I dont deny the mobspawners to drop heads. I only deny the player to get money for heads froms spawners

Hmm I see. Because only the chicken spawners seem to drop heads.

okay, but I dont chnage the behavior of the spawners. So it must be something else?

Not sure, but it's only happening for chicken spawners, all the default minecraft spawners don't seem to drop mobheads.