I've noticed that my rear derailleur (Ultegra 6700) will not return to where I've set the B-tension adjustment. Pulling it away from the hanger means it will just stick there, or maybe move back a little bit. Comparing to other bikes with Shimano rear derailleurs, mine seems to be odd one out.
It mostly causes annoyance when removing the rear wheel -- I have to push the derailleur back "in" afterwards, instead of relying on it just naturally going back to the correct position.