No oily scalp or itching here either, and I only get flaking if I whack way too much minoxidil on my noggin - shouldn't try to apply after a trip to the pub.
It's not really dandruff, more like unabsorbed minoxidil. Got it a lot when I started applying it 4 years back, then realised what it was and took care to spread the minoxidil out better. Problem solved.