Audio monitoring device doesn't persist when the default system output changes

Operating System Info

Other

Other OS

Arch Linux

OBS Studio Version

30.0.2

OBS Studio Version (Other)

No response

OBS Studio Log URL

https://obsproject.com/logs/0OOFA5P6KZWmV9Wx

OBS Studio Crash Log URL

No response

Expected Behavior

Monitoring device configured in Settings -> Audio -> Advanced -> Monitoring Device should be used for monitoring.

Current Behavior

When I switch audio output in GNOME top panel, OBS switches monitoring to the new system default audio output.

Steps to Reproduce

0. Have more than one physical audio output (e.g. internal speakers and USB headphones).
1. Set your default output to internal speakers in pulseaudio (e.g., using GNOME top panel menu).
2. pactl load-module module-null-sink sink_name=obs_record
3. Add an "Audio Output Capture (PulseAudio)" source that points to obs_record.
4. In Audio Mixer, open Advanced Audio Properties and set Audio Monitoring for the newly added source to "Monitor and Output".
5. Steer the audio output from some application to the obs_record sink (either in pavucontrol or in the application settings).
6. Go to Settings -> Audio -> Advanced -> Monitoring Device and set monitoring to USB headphones (or any output different from the one selected at step 1).
7. You should hear all system sounds in internal speakers, except the application from step 5 that you should hear in the USB headphones.
8. Switch the default audio output in pulseaudio (e.g., using GNOME top panel menu) to USB headphones and back to internal speakers.
9. Now all sounds are heard in internal speakers, including monitoring of the application, although it's still configured to USB headphones in the Settings.
10. If you toggle the selection in Settings back and forth, the monitoring resumes to USB headphones.

Anything else we should know?

No response

Start by reproducing the issue on Arch Linux with OBS Studio 30.0.2, following the listed PulseAudio and Monitoring Device steps. Investigate how the configured device behaves when the system default output changes. Done means monitoring remains on the device selected in Settings > Audio > Advanced, without toggling the setting.