Custom property desinger is not updating collection properties

//this is the class I'm using as a property on my control
    [TypeConverter(typeof(System.ComponentModel.ExpandableObjectConverter))]
    [Editor(typeof(Editors.DBBackgroundInfoEditor), typeof(System.Drawing.Design.UITypeEditor))]
    public class DBBackgroundInfo
    {
        public Color BackgroundSolidColor;
        public Color GradientStartColor;
        public Color GradientEndColor;
        [DesignerSerializationVisibility(DesignerSerializationVisibility.Content)]
        [ReadOnly(true)]
        public List<DBGradientStep> Steps;
    }
 
 
 
 
 
//this is the class which is stored in List<> property
    [TypeConverter(typeof(System.ComponentModel.ExpandableObjectConverter))]
    public class DBGradientStep
    {
        public Color Color;
        public int Position;
    }
 
 
 
 
//this is the instance of the DBBackgroundInfo class on my control              
        [ReadOnly(true)]
        [DesignerSerializationVisibility(DesignerSerializationVisibility.Content)]
        public DBBackgroundInfo BackgroundInfo;
 
 
 
 
//this is my custom type editor
    public class DBBackgroundInfoEditor : UITypeEditor
    {
        public override UITypeEditorEditStyle GetEditStyle(System.ComponentModel.ITypeDescriptorContext context)
        {
            if (context != null)
            {
                return UITypeEditorEditStyle.Modal;
            }
            return base.GetEditStyle(context);
        }
 
        public override object EditValue(System.ComponentModel.ITypeDescriptorContext context, IServiceProvider provider, object value)
        {
            if ((context != null) && (provider != null))
            {
                IWindowsFormsEditorService editorService = (IWindowsFormsEditorService) provider.GetService(typeof(IWindowsFormsEditorService));
                if (editorService != null)
                {
                    DBBackgroundInfoEditorForm modalEditor = new DBBackgroundInfoEditorForm();
                    modalEditor.EditingValue = (DBBackgroundInfo)value;
                    if (editorService.ShowDialog(modalEditor) == DialogResult.OK)
                    {
                        return modalEditor.EditingValue;
                    }
                }
            }
            return base.EditValue(context, provider, value);
        }
    }
 
 
 
//this is how DBBackgroundInfo is handled on the form which I use as property designer
    public partial class DBBackgroundInfoEditorForm : Form
    {
        private DBBackgroundInfo editingValue = null;
        public DBBackgroundInfo EditingValue
        {
            get
            {
                return editingValue;
            }
            set
            {
                editingValue = value;
            }
        }
 
        private void btnOK_Click(object sender, EventArgs e)
        {
            this.DialogResult = DialogResult.OK;
 
            editingValue.Steps.Clear();
            editingValue.BackgroundFillMode = copiedValue.BackgroundFillMode;
            editingValue.BackgroundSolidColor = copiedValue.BackgroundSolidColor;
            editingValue.GradientEndColor = copiedValue.GradientEndColor;
            editingValue.GradientStartColor = editingValue.GradientStartColor;
 
            this.Close();
        }
    }

                                  

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