UR5 self-collisions

Hello all, I'm using ROS and MoveIt! to control an UR5 robot arm. Sometimes the robot arm collides with itself. Is this a bug in moveit or the universal_driver package, or am I doing something wrong? I use the group.plan() method of the moveit_commander.MoveGroupCommander class (in Python). I've noticed that the Semantic Robot Description of the UR5 (ur5.srdr) has been changed since version 1.0.4 (indigo). A number of "avoid_collision" statements were added, that seem wrong to me. I think the following lines are incorrect, because the specified links CAN collide with each other: But even after removing these lines wrist 2 sometimes collides with the forearm. I don't understand why this happens. In rviz it can be seen that the links are colliding, so why is the path valid? Any information on this topic is very appreciated. Regards, Wouter