Hi:
Is your external interrupt set up correctly, both in HW and SW? The Mc13192 uses the external interrupt pin to indicate the GT60 to change modes. If the interrupt is not recognized, or clear, or never arrives, then the SMAC won't change mode.
There are also some issues with reentrancy of the interrupt code in the SMAC, and you might need to check the actual SMAC code and see if your code is not breaking something in the SMAC (variables, etc)
Regards,
Alex