Possible to leak memory even when you code doesnt contrain an alloc/copy/retain ?

Question

Possible Duplicate:
Memory Leak according to Instruments

I ran instruments on my code and it says I am leaking memory from one of my methods where I use substringWithRange. I checked my method and I use a couple of calls like the one below.

NSInteger theValue = [[data substringWithRange:NSMakeRange(i-rangeCount,rangeCount)]  
integerValue];

There are no allocs/copy/retains etc. I dnt see how I could be causing the leak.

Could it be a false-positive or what is it about substringWithRange that I am doing wrong?

Many Thanks, -Code