This is caused by the System booting faster than the ports can download their code and initialize. To solve the problem add:

		(
		until sleep 1 < /dev/ttya01
		do
		:
		done
		) 2> /dev/null

at the top of /etc/rc.d/8/userdef. If there are multiple devices, it may be prudent to replicate these commands for the first port on each device.