tty disappears on OS X 10.4.11

Hello,

my board is a new Arduino Micro, bought from an official distributor. On a PC with Windows Vista and Arduino IDE 1.0.2, both uploading sketches and receiving messages in the serial monitor window work as expected. So board and cable should be OK.

On OS X 10.4.11 the Keyboard Setup Assistant did not launch on the first or subsequent plugs. The Arduino IDE 1.0.2 starts without problems, but there is no serial port in the Tools menu starting with tty.usbmodem, just the bluetooth entries for my mobile phone, tty.Bluetooth-Modem and tty.Bluetooth-PDA-Sync.

I watched the contents of the /dev/ directory and also the System Profiler information, both during and after the board reset. The surprising result:
During the seconds of board reset with breathing LED, two entries tty.usbmodem5B1311 and cu.usbmodem5B1311 appear in /dev/.
In System Profiler the board is identified as Arduino Micro with product id 0x0037 and vendor id 0x2341.
But after the reset, both entries in /dev/ disappear! In System Profiler the product id changes to 0x8037.

There is no different result if I upload a sketch (from PC) with or without serial output, use a USB hub or plug direct into the computer. I even sat up a new user profile with admin rights on the Mac.

Following the system log after plugging the board:
Dec 9 23:27:11 MacMini kernel[0]: AppleUSBCDCACMData: Version number - 3.1.9, Input buffers 8, Output buffers 16
Dec 9 23:27:17 MacMini kernel[0]: 0 0 AppleUSBCDC: start - initDevice failed

I think this is an USB software problem between OS X 10.4.11 USB-CDC driver and the virtual USB serial driver of the Arduino.
Can anybody help?