Customizing Toolbar not Working

My understanding is that I should be able to right click on a toolbar item in order to have that item create a new group (which will then add a separator before it).

However, when I right-click on the toolbar, the nothing comes up - is this a bug or am I missing something?

(1) You need to be in toolbar edit mode.
Ie the View > Toolbars… dialog must be open.

(2) It must be a native toolbar, not a Ruby toolbar.
(They are different MFC window classes apparently.)

How to tell the difference ?

There is no right-click mouse context menu for a Ruby extension toolbar.