Once again (feels like the third time, but I'm going to refrain from counting) I reiterate that in tests where the arduino (and also pololu servo driver) are already powered on the issue persists. They are on separate supplies, something you assumed in post #6.
So while agree with you on your second point re. startup signals being for all intents and purposes random (or prone to give unexpected results etc.) - it would seem it is not relevant to this case - yes/no ?
Also:
- So you're suggesting I 'should' have 10 4k7 resistors on me? ...imminent shuttle disaster?
- You haven't explained what/how resistors would help - I think you said 'steady' the signal- I'm keen to learn (not being sarcastic). You're tying the line to GND - a pull down resistor?
- Did you by chance miss the part where the cap helped? i.e. likely just need another cap in parallel or a larger value single unit and I'm good
Phew ! something about some Arduino forum users that gets me going I tells ya.
Discussion is robust 