The following routine in StdCtrls has a bug

procedure TCustomComboBox.AdjustDropDown;
var
  DC: HDC;
  SaveFont: HFont;
  ItemCount: Integer;
  Metrics: TTextMetric;
begin
  DC := CreateCompatibleDC(0);
  SaveFont := SelectObject(DC, Font.Handle);
  GetTextMetrics(DC, Metrics);
  SelectObject(DC, SaveFont);
  DeleteDC(DC);
  ItemCount := FItems.Count;
  if ItemCount > DropDownCount then ItemCount := DropDownCount;
  if ItemCount < 1 then ItemCount := 1;
  SetWindowPos(Handle, 0, 0, 0, Width, Height + Metrics.tmHeight *
    ItemCount + 1, SWP_NOMOVE + SWP_NOZORDER + SWP_NOACTIVATE + // <-- on this line
    SWP_NOREDRAW + SWP_HIDEWINDOW);
  SetWindowPos(Handle, 0, 0, 0, 0, 0, SWP_NOMOVE + SWP_NOSIZE +
    SWP_NOZORDER + SWP_NOACTIVATE + SWP_NOREDRAW + SWP_SHOWWINDOW);
end;
 

The line should read

    (ItemCount + 1), SWP_NOMOVE + SWP_NOZORDER + SWP_NOACTIVATE +
    ^             ^
    |             |
    Note the open & close paren.  The effect of this bug is to force the Combo box to always show a scroll bar when dropped down, regardless of how many items are supposed to show.