The constitutional division of powers doesn't change, but the division in practice does. That's because the referred power remains residual - but the Commonwealth has the ability to use the power, within the terms of the referral act, as though it were concurrent. The power doesn't actually become constitutionally concurrent, though, because the Commonwealth can't use it for other states or outside the terms of the referral act; the state can also theoretically revoke the referral act and take the power back. The power is only 'exclusive' insofar as the state has voluntarily offered to stop legislating; so, not exclusive. It would be interesting to see the way the HCA would apply s109 questions, actually - because the state could in theory just amend the referral act to get rid of the inconsistency.
With referral, one of the interesting things is the amount of technicalities we haven't had proper HCA precedent on.