Maybe there's something wrong with your mac Word installation. I very much doubt MS would have added the button and then made it inoperative.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]

There is no button, there's just a blue bar that says "same as previous" on it. Someone else told me how to do it a while ago, and it worked, but I forgot what it was, and it's something obscure that I would never be able to figure out on my own.