When RadPanel is set to AutoSize, it should update its size automatically when changing the visibility of some control inside it.

Workaround:
 public class CustomRadPanel : RadPanel
    {
        public override string ThemeClassName
        {
            get
            {
                return typeof(RadPanel).FullName;
            }
            set
            {
                base.ThemeClassName = value;
            }
        }

        protected override void OnLayout(LayoutEventArgs e)
        {
            base.OnLayout(e);
            int maxHeight = 0;
            foreach (Control control in this.Controls)
            {
                if (control.Visible)
                {
                    maxHeight = Math.Max(control.Height, maxHeight);
                }
            }
            this.AutoSize = false;
            this.Height = maxHeight;
        }
    }