TIN MODEL - export of the XYZ as differences - ability to save either in Tin1 nodes or Tin2 nodes

When you create two models and want to export the differences into XYZ, there are checkboxes to either use Tin1 or Tin2 or Both as XY but they do not work i.e. if you check only Tin1, program should save the differences into Tin1 XY. AS John explained this never worked i.e. program always saves the differences into both models XY...