This is what I’ve found.
There is a small bug in the headphone preset edition. Fortunately there is a workaround.
Depending on how the recorder is configured you can route inputs pre or post fader to the headphone output, or just pre fader if you are not using the mixing facilities, ie, your gain settings are in basic mode. In that case you can make only selections that make sense.
For example, my recorder is configured as follows:
Channel: Advanced
Gain: Basic
Headphone: Advanced
Record: Advanced
Metadata: Advanced
Outputs: Advanced
I record only ISOs, not a stereo mix. So my headphone preset has inputs 1, 2 and 3 assigned to both headphone channels. Nothing fancy.
With the gain in basic mode it makes no sense to talk of LR mix, because the knobs become gain controls rather than mixer faders.
The bug is: I have tried to select the L and R channels from the stereo mix assigning them to headphone outputs and it works, while it shouldn’t. The trouble is, once I have selected them I can’t deselect them so I have effectively broken my headphone preset.
Fortunately there is a workaround: change gain to advanced mode so that the knobs become mixer faders again and hence the LR stereo mix makes sense, and you will be able to deselect them again.
I guess the same can happen if you have routed post fader inputs to the headphone outputs and you have changed gain to basic mode or something of the sort. I’ll report it to SD so that they can fix it in the next version.