Seeing that no creationist has attempted to answer this, I had a look through some creationist websites searching for their non-answer (I think I lost at least 200 IQ points in the process).
Anyway, the answer is easy. The Magic Fluddy did it.
Here is a 'scientific' article written by D. Russell Humphreys,
Ph.D. (the PhD is very, very important to them, it raises them to the level of God and therefore we have to believe every word of it),
explaining that the Fluddy reversed those poles a few times.