a port output error by stack overflow - VxWorks

hi
A problem by stack overflow just came to me.I created a user task for

process an exception.But the stack for the task is too small.The first size

i set is 1024 bytes.But the real needed size is about 1800 bytes.
Of course the stack overflow occurred.But an interesting problem

appeared.When the system suspended,a GPIO port(pc15) has been set high level.

If I added some debug code in the project（the stack size remained 1024 bytes

） and download.The stack overflow remained the same,but the pc15 output

level became low(I expected)!
Why this happened?
I'm using vxworks and the processor is powerpc.

regards,
Su_sword