Any loot from enemies killed by a group of players is not accessible and lost when the group setup changes (i.e. someone leaves) before the dead opponents are looted or even before everybody rolled on the goods. rebuilding the original group does not help.
Looks like loot rights are related to an abstact "group" object instead of the group members.
Already saw lots of blue and even some epic items been lost because of this bug.
Regular reported since more than 7 weeks, still not fixed.