Absolutely not normal.
Almost certainly a hardware fault. If you want to test this, boot a small, light linux distro from USB drive and see if the behavior persists.
If the mini 9 is under warranty, get it repaired. If not, you could try a replacement keyboard from ebay, or you could try dismantling the keyboard yourself, give it a good clean, and see whether re-seating the rubber pads under the space-bar stops the spurious spaces. It doesn't sound like a fault that could come from the other end (motherboard connection).