Shortly after I started using Windows 8, I noticed click & drag behaves differently when using a mouse vs a stylus.
With a mouse, the drag begins at the location where the cursor was when the button was depressed:
With a stylus, it appears that the drag isn't recognized until the cursor has traveled 10 pixels from where it first pressed:
(In the examples above I'm using Greenshot to try to screengrab a rectangle whose upper-left corner starts at the crosshairs in the background. I also encounter the issue in the Unity editor)
I'm guessing this was done to support the new touch features - when using an imprecise finger on a touchscreen, a user wouldn't want slightly wiggly clicks being interpreted as swipes.
But when using a more precise input device like a stylus, this can be quite disruptive. In drawing programs, a drawn stroke will fail to replicate the input stroke by a noticeable gap. When trying to drag items from a list view, the 10px error is enough to grab an adjacent item in the list instead of the intended one.
Unfortunately, my current problem is with the pen that came with my Surface Pro 3, so twiddling Wacom settings isn't available here.