turqoisehex wrote:Ok, thanks. I'll mark it as solved, though it seems strange to me that the functionality isn't included by default.
"gnome-system-tools" is a Gnome2 utility repackaged to run in a Gnome3 environment. The "User Accounts" utility built into Mint that does not allow you to manipulate groups is a native Gnome3 utility. Mint is using Gnome3 as a basis for it's redefinition of the desktop environment.
If I were to detail in length my true opinion of Gnome3 and the apparent lack of adult supervision of it's design process I would be banned from this forum. Let's just say that Gnome3 doesn't think you have a need to modify groups or if you do then you would already know how to do it from the command line.