For instance when I tried to export a very simple hidden line drawing to Freehand the background exported even though I was sure to exclude the background from the export. Another instance of a complicated hidden line model created an object in Freehand that would not print. In version 2.9.2 the file extension changed from .ILS to .AI to match Illustrator. Previously the grids and axes were considered background. Now they are not.
Background is simply a rectangle extending to the borders of the window.
When it is there and the image is placed on top of another, the latter is covered. When it is not, the image is transparent. If you do not want to export the grid and axes, you need to turn them off before Saving As in Illustrator. What is causing the object in Freehand that will not print we do not know. You will have to tell us more details to try to help.