http://en.wikipedia.org/wiki/Instant-runoff_voting#.22Return_of_the_3rd-party_spoiler_effect.22
Case 1: The spoiler effect only occurs here because it is a hybrid voting system. By only listing one preference, the voters are forcing a first past the post count for their vote. If they are required to rank all candidates (which is a rule in Australia) then this will not occur.
Case 2: Why is the apple candidate the winner? Both the apple and the grape have 45% of the primary vote. The banana was only mentioned by 31% of the voters so had no chance. Also, how is it possible to give the grape your first and second preference?
The only downside to IRV is failure to compromise. There is no spoiler effect.
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