thank you for reporting this issue.
This appears to be a dead link.
To do the defragmentation please start the Windows Explorer from the repair environment system menu. Then right click the drive to be defragmented and select properties and then the tools tab. There you will find a working defragmentation option.
yes this is a bug.
And it will be fixed before the release of Spybot S&D 2.2.
However it does not have a high priority since the defragmentation option is still available and because this is an additional option and not a core part of Spybot S&D 2.1.