Strange behavior datagridview

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C#

I came across a strange behavior by datagridview today.
It was when I was trying to attach a POCO model collection to gridview.
The POCO class is as:

class SchemaTaxClass
   {
       internal short ID { get; set; }
       internal short TAXCATEGORY_ID { get; set; }
       internal string NAME { get; set; }
       internal string ACRONYM { get; set; }
       internal System.DateTime EFFECTIVEFROM { get; set; }
       internal string DESCRIPTION { get; set; }
       internal System.DateTime CREATEDON { get; set; }
       internal bool ISACTIVE { get; set; }
   }

All properties are INTERNAL.

In main class I have:

public partial class TaxationUtils : Form
    {   
        List<Taxation.PrivateData.Schemas.SchemaTaxClass< _taxClassesCollection;
        Taxation.PrivateData.TaxClassCollection _clsTaxClassCollection;

        public TaxationUtils()
        {
            InitializeComponent();
            SynchronizeTaxClassCollection();
        }
        void SynchronizeTaxClassCollection()
        {
            try
            {
                GetOrRefreshTaxClassCollection(null);
                PopulateGridWithExistingTaxClasses();
            }
            catch (Exception ex)
            {
                AppendMsg(ex.ToString());
            }
        }
        void GetOrRefreshTaxClassCollection(short? taxCategoryID)
        {
            try
            {
                if (_clsTaxClassCollection == null)
                    _clsTaxClassCollection = new PrivateData.TaxClassCollection(taxCategoryID);
                _taxClassesCollection = _clsTaxClassCollection.GetTaxClassCollection;
            }
            catch (Exception ex)
            {                
                throw ex;
            }
        }
        void PopulateGridWithExistingTaxClasses()
        {
            dgv_ExistingTaxClasses.DataSource = _taxClassesCollection.ToList();       
        }
}

This is the Data Class from where we fetch data (through Entity Framework)

class TaxClassCollection
  {
      short? _taxCategoryID = null;
      bool FLAG_ERR;
      List<SchemaTaxClass> _taxClassList = null;
      internal TaxClassCollection(short? taxCategoryID)
      {
          this._taxCategoryID = taxCategoryID;
      }

      internal List<SchemaTaxClass> GetTaxClassCollection
      {
          get
          {
              FLAG_ERR = false;
              try
              {
                  GetTaxClasses();
                  if (!FLAG_ERR && _taxClassList != null)
                      return _taxClassList;
                  else
                      return null;
              }
              catch (Exception ex)
              {
                  throw ex;
              }
          }
          private set
          {
              _taxClassList = (List<SchemaTaxClass>)value;
          }
      }

      void GetTaxClasses()
      {
          _taxClassList = new List<SchemaTaxClass>();
          try
          {
              using (var _context = new vk1_0Entities())
              {
                  _taxClassList = (from taxClass in _context.TAX_CLASS
                                       where taxClass.taxZone_id == BusinessInfo.TaxZoneID
              }
              if (FLAG_ERR)
                  FLAG_ERR = false;
          }
          catch (Exception ex)
          {
              if (!FLAG_ERR)
                  FLAG_ERR = true;
              throw ex;
          }
      }
  }

What's happening is when POCO class members have internal as modifier, gridview doesn't display the data.
If modifier is turned to public, data is visible.

Why is such behaviour?

Remarks:
POCO class, data class and main class are all in same assembly and namespace.
Also, data is present in collection variable used as datasource for gridview.

What I have tried:

I tried exploring grid view from MSDN but found nothing that can justify this behavior.

When everything is in same assembly and namespace, internal must work.