Desktop audio fed into microphone input

For some reason, when I connect my headphones to my UR22C interface, my desktop audio is fed into microphone input. This doesn’t happen when I select Input 1/2 as my audio input (however, that’s recorded as stereo with only the left side having any sound) or when I reduce my Windows audio to 0 (with desktop audio still being picked up on OBS in the Desktop Audio channel, which is what I want).

How do I fix this?

That is not possible. There must be a different problem.

You need to clarify what your entire setup looks like.