Not many people have caught on yet or have noticed, But if two people are attacking the same monster, the one that delivers the finishing blow steals the kill and exp from the other player's pet. The other player may receive exp, but the pet receives zero cause the other player made the killing blow. This is a very common issue in the Goo Cube area since they are very weak but have a lot of HP and provide a lot of exp, more then sashquash. If anything the goo cube area is a common pet training ground once pets can deal with goo cubes.
Just figured if anyone that is not aware yet, or kinda wonders when someone gets pissed cause you butted in on a monster, well this is the reason behind it. I already made a post in bugs to get the exp split fixed, but.....