Until 22.214.171.124 the mainline kernel contained a bug whereby repeated opens of usb-serial devices using the ftdi_sio driver would fail to receive any data unless opened with the O_NONBLOCK flag set. Trying to fnctl( ) an already opened port would not resolve the issue.
This bug was fixed in the 126.96.36.199 update to the ftdi_sio driver and currently still affects the Ubuntu 2.6.31-14 kernel.
There was a not-insignificant update consisting of 4 patches to the ftdi driver in the .5 stable patch set. Can someone update this driver please?