Check this:

$$4 IC27154  3.7.3 SERVERS WILL NOT CHANGE THE STATUS OF A DRIVE FROM
LOADED
$$4
$$4  SYSROUTES:
$$4   IC27154(AIX37),IC27488(NT37),IC27489(HP37),IC27490(SUN37),
$$4   IC27587(AIX41),IC27588(NT41),IC27589(HP41),IC27590(SUN41)
$$4
$$4  TSM 3.7.3.0 does not change its state of the drive to empty
$$4  after the drive cleaning completes.  TSM tracks the state of
$$4  a drive as it uses that drive for a tape operation.  Because
$$4  the state of the drive indicates the drive is still in use,
$$4  TSM does not select that drive for another tape operation.
$$4