RE: Never Ending Charge
Yes. Almost certainly cell balancing.
I can't really see why it would not do cell balancing off the 10A lead but it is quite possible they have programmed it that way.
..and, yes, after cell balancing you can expect a better range. If you have been doing only part-charges for a while you need to do a 'full' charge and let it dwell so that the cells have a chance to fully balance. You only get the benefit of the least charged cell!
The thing I don't understand is why you say you could not release the lead from the car. Makes no sense. The only thing holding it on the car is the top clip that is mechanical and you press that button yourself. The only thing to stop you releasing it is a metal rod that activates just above the clip with the central locking. Was the car unlocked when you tried to remove the lead? If so, take a look to make sure the metal bar has withdrawn and then there is nothing preventing you releasing the clip.