Wim:
Sorry, not going to let you off the hook that easy!
I do show two distinct USB Display adapters when I have my two monitors attached simultaneously showing in Device Manager.
Also as previously mentioned, I was using this setup without issue until Windows 7, similar to others having problems shared in this thread. You do recall correctly that I have two 2263DX, each with a 7" DisplayLink USB display.
Hope you are still able to assist me!
PS Your suspicions about the Hardware IDs may still be valid, but it just doesn't explain how everything worked simultaneously while under Windows XP and not in Windows 7. The DisplayLink drivers worked under XP so we can't start blaming the manufacturer when the Win 7 driver doesn't. Well, I suppose we still can blame them