Serial.print messing with Timer Interrupts

Interesting! Here, you mean?

void MsTimer2::_overflow() {
	count += 1;
	
	if (count >= msecs && !overflowing) {
		overflowing = 1;
		count = 0;
		(*func)();
		overflowing = 0;
	}
}

So it relies on not missing those "overflow" ticks? I see what you mean.