Hi Alex,

The ButtonsRight collection is public and it gets serialized by the designer. So if you add a button to the designer in the combo1 class, then when you open the Form designer, the form designer will see the button and serialize it. The next time you open the designer, it will get added by both the combo1 designer code and the Form code.

This is basically one of the limitations of visual inheritance in Visual Studio. It will happen with any control that has a public collection. You can duplicate the same sort of behavior using Nodes in a TreeView control, for example.

I think you can get around this by not adding the button through the designer, but instead, add it in code in the OnCreateControl method. This way it only gets called when the control is created the first time.

    public partial class UserControl1 :  Infragistics.Win.UltraWinGrid.UltraCombo
    {
        public UserControl1()
        {
            InitializeComponent();
        }

        protected override void OnCreateControl()
        {            
            base.OnCreateControl();

            EditorButton editorButton1 = new Infragistics.Win.UltraWinEditors.EditorButton();
            editorButton1.Text = "a";
            this.ButtonsRight.Add(editorButton1);
        }
    }