Thanks for the reply.
It's bit weird this but I think I may have solved the problem.

I connected the Pronto to the PC and launched the simulator.
Then I ran every macro on the simulator at least once before downloading the PCF back to the Pronto.

This really does seam to ensure the macro runs properly. However, if iI reset the pronto or remove the battery then the problem comes back until I follow the above routine.

Definately a bug!