Linux Distribution: Ubuntu 16.04.1 LTS
In Virtualmin, clicked on "System Customization" then "Custom Links"
With "No custom links have been defined yet." -- Typed in a "Category Name" (such as "My Category") and clicked on "Save".
It continues to show "No custom links have been defined yet." -- Though the Category Name shows in one of the text boxes.
Without categories adding correctly we are unable to add links themselves.
Note: The previous version had the ability to add links without categories, which worked fine.