Unable to pan L/R in PT 10 on OS X
 

When listening to mono track in playback, panning does not work. Outputs are channels 1 and 2 and Apogee speaker outs are 1 and 2. When I switch Apogee speaker outs to 3 and 4 and change outputs in PT to 3 and 4, panning is again active. Don't understand why 1 and 2 are not functional.
I have tried restoring defaults in both PT I/O settings and in the Apogee settings as well to no avail.

Computer model and processor speed: MacMini 2.3
OS version: OS X
Avid hardware model: Apogee Quartet
Pro Tools version: 10
Amount of RAM installed: 4GB
Attached peripherals: All PT files are recorded to Glyph external drive.