Hi Wagar,
This is occuring because you have "Recycle = yes" configured in your Pool. This way, when bacula needs a volume, it will try to find one that had passed the retention period (in your case, 8 days). This is not a "volume name reuse", but a "volume reuse" because of your configurations.
If you want Bacula never reuse a volume, you just need to set "Recylce = no" and you can let your pool without the "retention period" configuration.
Best regards,
Ana