"Infinity of diamond helmets"

I was testing the command /gamerule keepinventory, for this i equiped myself with full diamond gear just to see the command working, then when i respawned after killing myself i spawned with an additional diamond helmet that wasnt there, then i throwed the helmet on the groud and when i tried to pick it back up, by stepping close to it my inventory filled up with diamond helmets, and by throwing them the same happens and i cant pick them up from the ground... i dont know from wich version that came but i was using the snapshot 13w04a when that happend.