Inserting files in montage

I have a montage with four tracks directed to four outputs. I want to put four files into those four tracks. So I place the cursor where they are to go, select the files, select the option to stack vertically, and select “Use existing tracks (create new if necessary)”.

The result is that the existing tracks are ignored, and four new tracks are created for the files.

Right. But in fact, the button is “inversed” (this is a mistake). Hence, uncheck it to get the behavior you expect.