Parent Pages: Why Does Content in my 'Based on' Parent Disappear when I Create a New Parent?

Hi All,

I've created a parent page in ID 17.3 with a simple footer text box at the bottom of each page in a two-page spread.

When I seek to add a new parent based on this parent page, the two text boxes disappear, leaving me with a blank original parent, and a blank new parent.
Any ideas as to why this is happening?

With many thanks,

Josh