bt headphones call ended on connect
Solution 1:
It turned out the problem was Skype. I have this running all the time and when you turn on your bt headphones it tries out the microphone as if it was in a call before ending the call. The problem goes away if you don't have Skype running. Alternatively, you can connect your headphones with skype open and then switch to its sound settings end switch things back to internal speakers & microphone. It seems to persist these settings even when you disconnect/reconnect the headphones after that.