It was defined as a "desired" resource, though it is not allocated at
all currently. Still, however, I am unable to allocate it to anything
else, and am able to see it on the OS of the LPAR that should have
released it.

I probably should have said controller rather than drive; but yes, I
have the controller that holds the drive unallocated from the first
LPAR; but am unable to allocate it to the new LPAR.