Bluetooth headset doesn't automatically connect when phone rings

I have an iPhone 5 with iOS 6.1.4 and frequently listen to music & podcasts via bluetooth to an LG HBS700 headset.

Here's the weird thing that I can't seem to find a solution to: I will be listening to a podcast [using the headset] when the phone rings. The podcast is interrupted and the ringing sound is played in the headset, complete with vibration on the neckpiece. Yet when I go to answer the call, the handset is defaulted as the audio source, not the headset. I have to fumble through to the "audio source" menu on the phone's screen and reselect the headset before I can use it to speak.

This doesn't make any sense at all...that the current audio device [the headset] that is IN USE AT THE TIME WHEN THE PHONE RINGS isn't actually used once I connect to the call, and I have to reselect it every time.

This behavior seems counterintuitive, that the active audio device in use at the moment isn't used for the phone call, too.

How can I solve this?

Thanks.