The keyboard shortcut for panning stereo tracks does not work as described in the Mixing section of the Keyboard Quick Reference Card. Instead, from either the Edit or Mix window, Option-clicking on the pan sliders of a stereo track sets the pan to "0" (center), rather than the default settings (hard left and right).This is a known issue. The keyboard shortcut will only bring the pan sliders of a stereo track to "0". You will have to manually adjust the stereo pan faders to hard left and right, the default position.