After downloading and installing Sonar Platinum, i noticed when the transport is changed to "large," there is a small graphical glitch in the record button.  You can float the transport and the glitch stays, so something may be wrong with the button image file.  This goes away when the transport size is changed to "small."  Anyone else see this?
 

Which version did you upgrade from? Different recording modes were introduced in X3, and that looks like what I would expect "Comping" mode to appear as.

Clean install on a Fresh Win 7 system.  Actually, I downloaded the Try Me Sonar Platinum Demo first and installed it via the Control Center, played around with it a bit, and then I uninstalled it.  I then purchased Platinum, and re-installed.

Ah, I see now.  So it's not a glitch.  Good to know!  I'm coming from Sonar 7 so this is a big leap for me.
 

If you right click the record button you can set the different recording modes. These changes are reflected in the GUI of the button.

Or click-hold (long-press) it.