The stty or ditty.dgnc settings do not stay configured on the ports and revert to 9600/8/1/None whenever the ports are opened/closed or after the system is rebooted.
It is typical behavior in UNIX to revert port settings to default values when a port is opened/closed.
Create a startup file that is executed after the dgnc driver module is loaded.
Here is an example, create and edit a file called: /etc/rc5.d/S95dgnc_ditty
The following entries, will configure the port for 4800 baud and software flow control for port 1:
cat < /dev/ttyn1a > /dev/null &
ditty.dgnc 4800 ixon ixoff -ixany ttyn1a
Link it to the /etc/init.d directory:
ln -s /etc/rc5.d/S95dgnc_ditty /etc/init.d/dgnc_ditty