Servo Tab Toggle switch not reliably toggling

The Flight Data screen's Servo tab's Toggle switch doesn't seem to be reliably toggling.

Here was how I saw the problem:

- load Copter-3.7.0-dev to the flight controller
- setup tuning page to show ch7out
- pressed Servo Toggle for channel 7

If the servo was high then it seems to go low, then high again, then low
If the servo was low then it seems to momentarily go high, then return to low

Reproduce the problem by loading Copter-3.7.0-dev, showing ch7out on the tuning page, and using Servo Toggle for channel 7. Start at the Flight Data screen's Servo tab and trace the Toggle switch behavior; done means one toggle produces the intended stable servo state change rather than a momentary reversal.

Written by the indexing model from the issue text.