Exactly One shouldn't apply to Model editing

(Bug, Investigate , Priority: High, Test Status: No automated tests yet , Reported By Bad Link: Thing 3y284of not found, )
Editor, Properties
Summary: User Story: When it's time to enter data into an instance of PagePanel, a Start Page and a Start Panel are both required; it's not a valid reference if either is blank. Hence, I have marked those as Exactly One. So far, so good.
When I edit the MODEL, however, I very much DO want to leave these fields blank. Any value I entered would be incorrect most of the time, requiring extra keystrokes and attention to delete it. Unfortunately, the editor will not currently let me do this.
If you think that required-at-the-model-level is necessary for Apps, it should somehow be separated from required-at-the-thing-level.