Linux Prolific USB-Serial question

I am developing support for the SPH-N400, which uses a cable with,
apparantly, a PL2303 chip in it. Under windows, I have installed a driver
from Prolific's website. The test packets that I readback with
self.comm.writethenreaduntil look as I would expect. But under linux,
(Fedora Core 1, pl2303 module, /dev/ttyUSB0, same code), the data that I get
back is missing the first two bytes.

Anyone seen anything like this under linux for other phones that use the
prolific 2303 module?

Stephen