Did you check the output routing (Home->Output Patch->USB Audio)? I guess the Windows control panel only shows the first pair of audio streams, which are coming from first two channels by default. If you want to record stereo from LR you either need to record streams 17&18 or change the routing.
Thanks Andreas, this is helpful. Since I’m not using a DAW, I don’t have control over specific channels, only what Windows WMD/Direct X is fed. I’ll try patching everything to the first two channels.