Seems like if VC viewpoint is unstable for any reason, like turbulence or TrackIR usage, then it is easy for GTN VC gauge to interpret a click as a drag, since the mouse pointer does not move with the plane.

 

I've found myself either locking viewpoint or resorting to popup - They are otherwise too small to read on a 1600x900 notebook screen anyway.

The inability to pan the map in VC is an FSX bug, those not experiencing it are likely using P3D where the bug has been fixed. From the GTN developer:

 

 

 

This is a known FSX bug, it is the mouse position calculation function that is not calculating the coordinates correctly. This is a FSX bug and we can't do anything about it, we ask our customers to post this bug to FSX Steam, hopefully they will solve it. This bug has been solved in P3D. The best solution is to look perpendicular to the GTN in the VC. This does not have to do with the GTN PC Trainer.

 

(IMHO the best solution in FSX is to use the 2D pop-up, I've seen the "perpendicular trick" work exactly one time)