Persisting property grid collections with default values

I have a treeview that I want to come with certain collections. I'm having trouble getting my collections to persist, I suspect because they have default values. Am I correct? Anything I can do? What follows is some code:

[TypeConverterAttribute(typeof(System.ComponentModel.ExpandableObjectConverter))]
        public class NumberCriterion
        {
            private string _Title, _Format;
            private bool _Multi;
            public NumberCriterion() { }
            public override string ToString()
            {
                return _Title ?? base.ToString();
            }
            [DisplayName("Title")]
            [Description("The unique title of the criterion.")]
            public string Title
            {
                get { return _Title; }
                set { _Title = value; }
            }
            [DisplayName("Format")]
            [Description("The criterion format.  {0} is the field name.  {1} is the value. {2} is the optional additional value.")]
            public string Format
            {
                get { return _Format; }
                set { _Format = value; }
            }
            [DisplayName("Multi")]
            [Description("Indicates that the user specifies two values.")]
            public bool Multi
            {
                get { return _Multi; }
                set { _Multi = value; }
            }
            [Browsable(true)]
            public NumberCriterion(string Title, string Format, bool Multi = false)
            {
                _Title = Title;
                _Format = Format;
                _Multi = Multi;
            }
        }

static NumberCriterion ncRdlEquivalency = new NumberCriterion("Is", "Fields!{0}.Value = {1}");
        static NumberCriterion ncRdlSucceeds = new NumberCriterion("More than", "Fields!{0}.Value > {1}");
        static NumberCriterion ncRdlPreceeds = new NumberCriterion("Less than", "Fields!{0}.Value < {1}");
        static NumberCriterion ncRdlBetween = new NumberCriterion("Between", "(Fields!{0}.Value >= {1} AND Fields!{0}.Value <= {2})", true);
        static NumberCriterion[] RdlNumberCriteria = new NumberCriterion[] { ncRdlEquivalency, ncRdlSucceeds, ncRdlPreceeds, ncRdlBetween };

[Browsable(true)]
        [Editor(typeof(System.ComponentModel.Design.CollectionEditor), typeof(System.Drawing.Design.UITypeEditor))]        
        [Category("Criteria"), DisplayName("Numbers")]
        public List<NumberCriterion> NumberCriteria
        {
            get { return NumberFormatList ?? RdlNumberCriteria.ToList(); }
        }