diff between updating and adding custom page

Folks:

I'm administering two PF 7.00.05 sites in parallel. I need to add a new custom page to each. In Admin Panel--> Custom Pages...

For Site A, I pasted the new content into the Page Content box, added a new (and unique) Page Title, and accepted the defaults for everything else. Then I clicked on "Save Page". PF cleared the data and gave me a confirmatory message


For Site B, as far as I can tell, I did the identical sequence, but instead of getting a new page, PF overwrote an existing custom page. Which one? I think it was the one listed in the Current Custom Pages setting at the top of this page.

Since this page combines access to existing Custom Pages and adding new ones, I looked for a way to "disable" referencing an existing page, say, a top pull-down menu item like "[new custom page]". Or a checkbox that says, "New Custom Page". But I didn't find anything like that. I'm sure I used a new, unique page title for Site B, but that failed to tell PF, "I want a NEW page".

I can't figure out how to distinguish between updating an existing custom page and adding a new custom page. There's got to be a foolproof way to avoid overwriting existing content. Is there something really obvious that I'm missing about the user interface? Or what?

TIA
hen3ry