Was it a four or not?

I wondered watching the cricket vs Aussie why, despite hitting a four when on 336, NZ only scored 337. The four looked clear as.

A thread on Public Address suggests the answer. As the batsmen had already done one run, before the ball crossed the boundary, the game was ended at that point and hence the four was never scored.

Seems somewhat unfair to the batsman.

Anyone know the rules well enough to cite them for this sort of situation?