I thought at first also about the ribbon cable (is only one). Dismounted and cleaned it, but after a while it starts again (but not always and if, not so long).

What I found out meanwhile:
The device binded to port 1 is device "USB Receiver". No glue what that class is doing....has to do with HID.
see pic. There you can also see the error messages.
46643356oi.jpg

I'm not at home till monday. Then I'll test it with OSX and with external keyboard too. And, I think I have an older PB-QWERTY-Keybord to test - have to search for it.....