Not a feature I'm interested in TBH, but I tested it for you anyway. It does stop the playback pretty quickly, only a fraction of a second after disconnecting my bluetooth headphones. However it also stops playback when switching back to my bluetooth headphones, and also a couple of times when I had the daemon running the audio didn't actually switch to my bluetooth headphones after they connected.

I couldn't find the option for the feature in openmediaplayer to compare it against, I'm running what appears to be the latest version in the repo (20120326-1), is it only in a newer version available elsewhere, or am I just being blind and can't see it.