From the sounds of that, it works opposite to my thinking, and going "short" on the ZAR not the same as shorting the ALSI?
I don't know much about forex but I think, if you short the ZAR/USD for example, then you're expecting the Rand to weaken against the Dollar, so you're selling the Rand, buying the Dollar..and the interest is positive if the US interest rate is greater than the SA interest rate. But as our rates are higher than the US, the interest should be negative and you'll have to pay. Maybe, I'm not sure about this, its interesting, I'll do some research on it later on.