Headphones not detected if plugged in at boot

No red light in the jack in this situation.

Seems to happen either at boot or when coming out of sleep / hibernation with the headphones plugged in.

I think I now know what the issue is, but no idea how to solve it.

I believe what's happening is that when laptop has the headphones plugged in and the connected Thunderbolt Display is turned off (after a half hour or whatever), when the screen turns back on - its speakers get detected and for some reason the OS thinks that the "new" Thunderbolt speakers should be used instead of the plugged in headphones.

So I found the solution through experimenting.

• Open the "Intel Iris Graphics Control Panel"
• Go to the "Audio Settings"
• Enable "Audio Without Video" (allows sound to keep playing after monitor blanks out for power savings).

What happens here is now when the Thunderbolt Display goes into to sleep mode - the audio doesn't get turned off which has the desired effect of when the display gets turned back on from sleep - the system doesn't mess with the audio - it leaves your plugged in headphones as the selected source. Without setting this, I believe the system sees the display's audio as a "newly connected" device when it comes out of sleep and switches to it.