How to reproduce:  subcribe to the Click event handled of a RadSplitButtonElement added to a certain group in RadRibbonBar, notice that when you click on the button the event will fire two times

Workaround: 
bool cancel;
private void radSplitButtonElement1_Click(object sender, EventArgs e)
{
    if (!cancel)
    {
        //Handle Click event;
        this.cancel = true;
        return;
    }

    this.cancel = false;
}