I just had the same situation yesterday. My mother was listed in the 1940 census as living with my grandparents. She was also listed as living with her older sister Mattie and her family. The odd thing was, my Aunt Mattie was the enumerator for both pages. I'll never figure out that one.
Anyway, when I went to add the second census page for 1940, there was a small little block on the left side that said: New Event. I checked it and the census was created as a separate event from the one already generated. On the profile page they are listed one after the other with the same date.