If I share my queue with another user then claim an item out of a group queue, the other user cannot see that claimed item. This is true even if the other user is a member of the same group. The ACL is set properly. The same process will work as expected if assigned to an individual user, just not to a group queue. I have members of the same group who shared each other's queues with each other specifically for the purpose of grabing an item back that was claimed.