If you pan an instrument all the way to one side and you can still hear on the other side, it is because the Stereo Stage feature is on (cc103).

When Stereo Stage is turned on it adds calculations that simulate the arrival times from the position of the instrumental sound source to a pair of virtual stereo microphones plus the first reflections from side walls, rear walls, and ceiling.
This can create a more three dimensional image for positioning instruments on the stereo stage, both left to right and front to back, especially for monaural instruments (e.g. solo instruments that lack recorded stereo information.)

There are two options if you want to get wider a panning: Turn off Stereo Stage, using the power button (cc103) in the Controls tab or lower it's depth level to taste using the Depth knob (cc36).