I found adding a call to `set_maximum_size ' and `disable_user_resize' before adding the container fixes the problem, but I think you will agree with me that it shouldn't be necessary to do that. Note that just using a call to `set_maximum_height' will not work.

box := new_border_box
dialog.set_maximum_size (box.width, box.height)
dialog.disable_user_resize
dialog.put (box)