"Audio source" option is missing; no audio to headset

Hi all,

iPhone 4S, now on 5.1.

This problem started recently. My bluetooth headset connects, and can trigger the call to be answered, but the iPhone doesn't use it as the audio source. In fact, the button that normally selects the sources, now shows only the speaker icon (and toggles speakerphone).

After updating to 5.1, it seemed to be fixed -- that same button again let me choose the audio source. That was yesterday, but today when I answered a call, it didn't go to the headset, and the source button again shows only the speaker icon.

The iPhone answers the call when I press the button on the headset. It's just not seeing any audio source.

I've powered on & off, not fixing the problem. I can't poinpoint the start of the trouble exactly -- it seemed to simply work one day and not work the next. I honestly don't remember if it coincided with updating to 5.01.

Is anyone else seeing this?

B