[Mark McLeod]

The likeliest possibility I can think of is that the robot isn't left to sit still long enough the second time through to allow the gyro to initialize and establish a zero movement point.

I should have addressed the matter of Finish.vi, since you asked and you say such nice things.
Normal robot operation/termination never goes through Finish.vi.
The power just gets cutoff and the code ceases mid-execution.
The Stop sign on Robot Main functions the same way.
That big "Finish" button in Robot Main is the only way that Finish.vi ever gets executed.