I cannot reproduce this here.
I added 3 items at design-time and then have at runtime:
procedure TForm1.Button1Click(Sender: TObject);
begin
AdvDBComboBox1.Items[0] := 'Niedrig';
AdvDBComboBox1.Items[1] := 'Mittel';
AdvDBComboBox1.Items[2] := 'Hoch';
outputdebugstring(pchar(advdbcombobox1.Items.Count.ToString));
end;
and I still see 3 items and it reports also that Items count is still 3.
Do you use the latest version of this component?