When audio devices connected or disconnected from the system, the default audio device swapped around. This was because of QML setting index 0 on ComboBox.model changes. onCurrentIndexChanged was calling setPlaybackDeviceIndex() / mirrorDevice/ micDevice etc... in the audio tab controller and actively setting the audio device index to 0 momentarily. Changing onCurrentIndexChanged to onActivated allows the ComboBox to only actively command the audio tab controller in direct response to user interaction.
Kung-vr