Many thanks!
We'll change Opus to ignore these, but if you expand that Network branch in regedit and delete the empty B, D, F and S keys there (only leaving the Z key which has something in it), then reboot, the unwanted drive letters should go away.
Since they are empty, they won't be doing anything and are safe to remove.
(Why something has created those empty keys in the registry, or failed to clean them up properly when removing them in the past, I am not sure.)