I had been running Energy ROMs which are pretty good and had the hangup issue but I decided to give Calkulin's Kitchen a go (he also builds ROMs too).
My hangup hang over bluetooth with data active is gone
I am not running the data disconnect tweak.
See my signature for a link on how to basically use the Kitchen along with everything you need to build what I'm running.
It may not be the bluetooth stack after all causing the hangup issue with data session active.
I have no idea what fixed it, I stripped a bunch of stuff out of the custom ROM I made. Or it may be Calkulin's customizations that fixed it. A lot of odd things are fixed too. I don't know what was the specific thing that fixed, all I know is it works now. It might not solve other blue tooth issues folks are having though.
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EVO 4G, Stock Sprint ROM, ProClip in Car, Sony HBH-300.