Extended Keyboard with iMate and Yosemite

My Extended Keyboard II with German layout connected via iMate works for all keys - except one: the ^ key (it is below the ⎋ Escape key and left to the 1). The key-switch is OK, the LED in the iMate lights up when pressing the key, but since 10.4 or so, it never worked. Must be something in the system keyboard layout detection! It also shows up as a small keyboard without number pad when displaying the layout.

BTW: It is a dead key, as is the ´. It does not work as a dead key, as well.

What a pity! I'd love to use that old keyboard again, it was the best Apple ever made. Any idea how to fix it? I'm currently on Yosemite.