Unwanted Save Prompt In Access 2007 Forms

I have several simple continuous forms in my Access 2007 database that
are bound to tables that contain lookup lists. If I open one of these
forms, select a record, hit Delete and then cancel the delete at the
confirmation dialogue, when I close the form I am prompted to save
design changes to the form. As far as I can tell, all continuous
forms in the database are behaving the same.

I haven't done any design changes. What gives? Am I missing
something here?