We asked you what button type, you answered
The button type is jqbtRadio.
And that was implemented, ie, the javascript translation for Checked.
The Checked property only have meaning for CheckBox or RadioButton.
the buttontype button, it's for normal button with no relation with the others.
And GroupIndex is only for radio buttons.
More info here
There is a typo in the documentation, jqbtNormal,jqbtSplit was replaced by jqbtButton, since the very beginning and was never updatedin the docx.
Happy weekend!