RadCheckedDropDownList selected items not being stored to dataset

I have a list of people in a datatable that I bind to a RadCheckedDropDown list via a bindingsource. This control is sited on the first page of a tab control. It's a list that provides the app user with a definable selection of staff members for a report.
On initialization of the form, only one item is selected, but as a test I check all items in the dropdown then move to the 2nd page of the tab control. If I then return to the first tab, the checkeddropdown list has returned to displaying only the initial single checked item .

I placed a breakpoint in my code and the dataset hasn't changed, ie the "Include" field still remains set to false for all rows except that initial row. ie checking items in the list aren't being reflected in the dataset. See untitled2.png

Have I failed to do something ?

      // 
      // CmbStaffFilter
      // 
      this.CmbStaffFilter.CheckedMember = "Include";
      this.CmbStaffFilter.DataSource = this.bsStaffFilter;
      this.CmbStaffFilter.DisplayMember = "Fullname";
      this.CmbStaffFilter.ItemHeight = 32;
      this.CmbStaffFilter.Location = new System.Drawing.Point(29, 35);
      this.CmbStaffFilter.Name = "CmbStaffFilter";
      this.CmbStaffFilter.ShowCheckAllItems = true;
      this.CmbStaffFilter.Size = new System.Drawing.Size(444, 20);
      this.CmbStaffFilter.TabIndex = 121;
      this.CmbStaffFilter.ValueMember = "RecId";

      // 
      // bsStaffFilter
      // 
      this.bsStaffFilter.DataSource = typeof(pulse.move.datasources.dsFilterStaff.dtFilterStaffDataTable);