The LineVisible parameter should be defined to False in the OnGetMenuExtraLineData event:
procedure TForm1.sSkinManager1GetMenuExtraLineData(FirstItem: TMenuItem; var SkinSection, Caption: String; var Glyph: TBitmap; var LineVisible: Boolean);
begin
// Check a first item in popup menu
if FirstItem = Multilinetext1 then begin
// Show line in this SubMenu
LineVisible := True;
Caption := 'Additional information bar'
end
else
LineVisible := False;
end;