Group Loot is not working, it is working like Need Before Greed, but it shouldnt.
Group Loot should work like this:
When an item equal to or above the threshold (details on threshold below) is on a monster that is killed, everyone gets a pop-up box on their screen with the item and pass or roll options and a timer. Anyone who rolls, displays a number between 1 and 100, the highest roller of all those who choose to roll automatically gets the item. Anyone who waits until the timer expires automatically passes. Items below the threshold are taken care of by normal round robin rules. If more than one player ties a loot roll, a random player will receive the loot. An interface option, "Detailed Loot Information" is defaulted to 'on.' If you turn it off you will only see the roll and Need/Greed option of the player who won the item rather than information for every player.