Hello,
sorry for not coming back to you earlier, I did not have access to the
oscilloscope until now. The issue is resolved by the folowing commit to
the kernel:
108e02b12921078a59dcacd048079ece48a4a983
(usb-ftdi_sio-fix-initial-baud-rate.patch)
Applying this as a patch to the kernel solves the problem for me.
Thank you very much for your time,
Andreas