The inventory had to be an offline inventory probably to cover your scenario
which is nasty.  Like we said the CE did the wrong thing.  An offline
inventory should have put the tape in a status of missing (not FF00).
However, your issue was in TSM all along.  If you had marked the tape as
unavailable in TSM with the

UPDATE VOLume
DELETE VOLume
MOVE Data

as appropriate you would have not had a problem with TSM.  It depends on the
state the volume is in at the time of the condition.

However, if it bothers you that the tape would be in the library inventory
as missing, then the way you did it is the only way to fix the problem.