To reproduce:

            this.radPropertyGrid1.SelectedObject = this;             
            this.radPropertyGrid1.PropertyGridElement.SplitElement.HelpElement.MinSize = new Size(0, 60);

Please refer to the attached gif file.

Workaround:

            this.radPropertyGrid1.SelectedObject = this;             
            this.radPropertyGrid1.PropertyGridElement.SplitElement.HelpElement.MinSize = new Size(0, 60);
            this.radPropertyGrid1.PropertyGridElement.SplitElement.HelpElement.HelpTitleElement.MinSize = new Size(0,20);

            this.radPropertyGrid1.PropertyGridElement.SplitElement.HelpElement.HelpTitleElement.PropertyChanged += HelpTitleElement_PropertyChanged;

        private void HelpTitleElement_PropertyChanged(object sender, PropertyChangedEventArgs e)
        {
            if (e.PropertyName == "Bounds")
            {
                if (this.radPropertyGrid1.PropertyGridElement.SplitElement.HelpElement.HelpContentElement.Location.Y != 20)
                {
                    this.radPropertyGrid1.PropertyGridElement.SplitElement.HelpElement.HelpContentElement.Location = new Point(0, 20);
                }
            }
        }

Note: the description element may be floating but it doesn't overlap the title.