Hi Mike,
I wouldn't describe it as a non-issue per se. Perhaps more an uncaptured requirement (if required) or an undocumented feature (if not required), either way, although it is inconsistent with JTA I suspect it won't make it into the initial version. If you do think it might be vital (from a user expectation point of view) you can raise it as a child of JBTM-895, alternatively someone (either distributed EJB or transactions) must document this restriction.
Tom