I actually use that feature all the time. I have a Bluetooth music adaptor in my car that I stream music to. When I go into a store or something and want to continue to listen to music without pausing I just plug my headphones in.
It was the same way with my former iPhones, Galaxy S3, Droid Incredible 2, Droid Razr Maxx, HTC Hero, etc. I think they do this by design and not really a "flaw." They probably think that is you have something plugged into the headphone jack then that's where it needs to go, otherwise why not just unplug it?
Just my observation over the years of having multiple devices.