Webmin --> Webmin Users , i have a webmin group; if i select a user and click on [Add to Group:] , button work like the [Delete Users] button.
And got: Failed to delete users : One of the selected users is marked as non-editable.
Webmin version 1.760
Virtualmin version 4.18
Theme version Authentic Theme 16.01
PS: I tried a fresh virtualmin install on a local vm, issue is present only with virtual server .. without virtual server button work as expect.