dupe bug

yesterday i did maps with my friend and i went back to sell the item, after i sold the item, i was empty, i enter the portal for the map and i get the game closed, when i relog, i see the portal where i went dissapear and in my invetory i found the same item that i sold to the guy like 5-10 sec before, idk why but sometimes the game closing automacly, sometime it happen when i enter in the new map, i didn't know that this could happen