On some machines, the printer port (but not usually the modem port) can receive
spurious characters when transmitting at high speed.  The default serial port
setting echos these characters into the output stream, causing glitches.

#stty -echo < /dev/cua1    (monolothic)
#stty -echo < /dev/cua0    (MkLinux I'm guessing here, since I don't have it)

Stops the echo, fixing the problem.  Note that the 'raw' option to stty does
not turn off the echo by itself.