Ah, thanks for checking.
In the meantime I have discovered here what had caused the behaviour for me in Firefox:
In Firefox you can configure what shall happen with what filetypes, and I had set "LDRAW Part" to "Save",
because this is the only thing I want to do when working with files from the PT.
Thus, the saving of the DIFF result was in fact a proof that the LDRAW server sent the proper information.
In the meantime I have discovered here what had caused the behaviour for me in Firefox:
In Firefox you can configure what shall happen with what filetypes, and I had set "LDRAW Part" to "Save",
because this is the only thing I want to do when working with files from the PT.
Thus, the saving of the DIFF result was in fact a proof that the LDRAW server sent the proper information.