Copy container pool tape volume reclaimed but not deleted from stgpool

[Mita201]

LTO8 volume of an container-copy stgpool in TL has been reclaimed by "protect stgpool", but never deleted from stgpool (several days already, 0 utilization)
REUSEDELAY is 0, on both, container copy pool and on protected container pool, as well.
Checked actlog from the protect stgpool process, it says reclamation was complete and successful.
What may be the cause for keeping the volume in stgpool even when empty?
ISP 8.1.15

Thanks,

Mita