PRV Track Zoom/Scroll is sluggish when controller views are open

I'm experiencing a sluggish/non responsive behavior when trying to scroll left to right or using Time-Ruler Zoom tool in PRV while having Velocity and any other controller visible in PRV editor. (running Dorchester build)
 
steps to repro:
1. Open PRV with one midi track only
2. Slide the controller view up to show Velocity only. Notice scrolling left to right and Time ruler zooming is fluid and smooth.
3. Add a second controller to show under Velocity (like Sustain or Mod Wheel). Now scroll left to right or use track zoom tool. The action is sluggish and response is delayed.  
4. With both velocity and mod/sustain controllers added, minimize the controller view by dragging it down to bottom of PRV so it is not visible. Notice the scrolling is now fluid and responsive again. 
 
Something is weird about displaying that controller data.  I pretty much have to revert to SONAR X3 until this is fixed because it is completely debilitating.

Is anyone else experiencing this?  If there is something in the settings I need to adjust, please let me know!
 
Thank you!
 
PC Specs: Gigabyte GA-X58A-UD5, i7970 3.2ghz, 24G memory, 7200 RPM Hard disk OS. Windows 7 SP1 64 bit.