[twcho]

This question is interesting enough and I've seek my pd's opinion on it. I am quite persuaded by his argument.

4D should be non forcing, reason as follows:

If 4D intends to be forcing, then it must be slam try. If one want to slam try with D fit, surely he must hold control for at least one major, then why can't he bid 4H or 4S instead of the ambiguous 4D. So 4D should be non forcing.