There has been a problem with the drop-rates of the Mutation-set items.
This file fixes this problem.
The Mutation items will now drop at the same rate as regular set items.
As a future project, I plan to adjust the drop rate in a different fashion, so they drop less frequently without them not dropping at all.
Backup the drop.txt file from your "install path"\scripts\server folder.
Copy or move the downloaded drop.txt in that folder.