I have some input, which might interest you. Me too, I experienced
serial problems in 2.1.9, and noticed that they were due to a mis-set
UART type. The UART was correctly detected as a 16550A during
boot-up, but then it was set to 16450 from /etc/rc.d/rc.serial
(probably a left over from my previous modem). After I removed the
offending line from rc.serial, all was fine and dandy again. Thus, at
least some of the serial problems, maybe be due to a misconfigured
UART type.
Regards,
Alain