I've been seeing similar problems on ubuntu 9.10, but not on 9.04. unplugging and re-plugging the device usually fixes it [although if you have the same buggy ftdi driver as me, the /dev entry will change because it can't clear the old one out].
If I try connecting to the port by hand, then it works for a while and then suddenly turns to garbage after typing for a bit.
Thus far, it seems like this is another 9.10 manifestation-of-bugginess
You might also try explicitly passing the --baud=9600 option, see if that helps. It shouldn't make a difference, but I have yet to see 9.10 ftdi-sio properly work right, at all.