I got a new firmware for the docking station from hp. It seems like that the firmware fixed our problems.
The ftp Link from HP for the firmware is not working anymore, but I uploaded it to dropbox.
You need to download the "TeslaUpdater-7.61" and "tesla_firmware_hp_Ver2_30_000.zip". Unzip the folders, start "TeslaUpdater.exe", choose the firmware file "tesla_firmware_hp_Ver2_30_000.eeprom" and follow the instructions.
As far as I know, you need a monitor connected with displayport during the firmware update.
Please let me know, if the firmware update was helpfull.