It seems that not only did some democrats vote in the Michigan republican primary, satan himself also voted. Check the primary results in Mackinac county (e.g. on http://elections.msnbc.msn.com/ns/politics/2012/Michigan/Republican/primary at least this was the data on wednesday)
The final result in that county was very close. It was by one vote for Romney, but you should check how many votes did Santorum get:
Romney: 667 (41%)
Santorum: 666 (41%)
