Timer toggling the led at ST1_55 13th bit

After the timer expires I toggle the led.

When GPT_start(hGpt) is called the led is turned off.

Why is bit 13 of address 3 cleared on that call?

The timer is about 3 seconds which should be lots of time.

The code works fine when single step except when GPT_start(hGpt) is called.

Thanks