Reproduced the issue on 4.9.0 and verified the issue on upstream release-4.9 - The disk is deleted if the "Delete disks" is checked. - The disk is not delete if unchecks the "Delete disks".
Since the problem described in this bug report should be resolved in a recent advisory, it has been closed with a resolution of ERRATA. For information on the advisory (OpenShift Container Platform 4.9.7 bug fix update), and where to find the updated files, follow the link below. If the solution does not work for you, open a new bug report. https://access.redhat.com/errata/RHBA-2021:4579