problems with unsigned long

Hi,

I'm having a problem using unsigned long.
Im using the LARGE memory model.

unsigned long largeWait;
largeWait = 10000;
while(largeWait--);

when I run this on my chip I never exit the loop.
Any Ideas? Are there known bugs concerning unsigned long?

this code for example works:
unsigned long data largeWait;
largeWait = 10000;
while(largeWait--);

this code works as well:
unsigned short largeWait;
largeWait = 10000;
while(largeWait--);

Thanks