Quote from def:
i'd laugh, but this happened before. one of the exchanges we trade accepts margin in a few currencies - including Yen. a while back the exchange took a haircut of 2% (yes it was a crime) off of interest paid on the margin deposits. Naturally it made sense to fund in Yen and avoid the haircut. (for obvious reasons it didn't last long)
Before I laugh; I had better check our statements ...