2006 town car door locks

When I go to unlock my doors on 2006 TC I push the switch and all locks come up, however, the rear doors are not unlocking all the way. The only way I can get the doors to unlock is to pull up on the knob as I push the switch at the same time and the doors will unlock and become funtional. Where is the problem? Thanks

Where is the problem?

I would first try removing the little chrome knobs temporarily and operate the locks to see if they go full travel with those obstructions gone..