Strange behaviour setting pinMode by array

[Grumpy_Mike]

@serious_sam

Oh, and if I take that malfunctioning code, and just add pinMode(10, OUTPUT); after the pinMode for loop, it works correctly:

So as your setup function says:-

@serious_sam

for (int i = 0; i <= 9; i++) {
    pinMode(PINS[i], OUTPUT);
  }

You are not initialising pin 10, the last value in your pins array.

Try

for (int i = 0; i < 10; i++) {
    pinMode(PINS[i], OUTPUT);
  }