Heh, this is funny...
The irivers only record stereo atm, and have no setting for that in the recording settings screen. The option however still exists in the settings struct, and is used to write that text on the screen. The default value (0) means stereo.
So somehow the settings of user got changed/bad, causing it to display mono.
The value is not used however, recording is always done in stereo.
Tip for user: reset your settings (hold rec just before rockbox boots, it will say 'settings cleared')