FYI, I’ve found a bug with SBP 2010 while using a 21UX Cintiq.
At times when using either the ellipse or straight ruler, when clicking on the handle to move the ruler, it will jump and/or reset to the center of the screen. After that event the stylus responsiveness setting under the Edit menu will reset back to the left.

I’ve been able to repeat it many times but have yet to understand what causes the rulers to reset.
I am not sure if this is a known issue, but I thought I’d share.