Items not stackeable

Hi!
Well the problem is that when a player mines o picks some items and disconnect
the new items the get they don’t stack, i have the last version of AuthMe, its
http://www.spigotmc.org/resources/authme-reloaded.6269/history i have the last one
i have Multiverse-core the last version http://www.spigotmc.org/resources/multiverse-core.390/history

 

I have been looking and they said that i try old and last version of authme, but it still happens

 

I check Multiverse core, all of the config, and i cant see any anti-stack :/