Deleting an element of a Set of Model Type can cancel the whole edit

(Bug, Investigate , Priority: Critical, Test Status: No automated tests yet , Reported By Bad Link: Thing 3y284of not found, )
Editor
Summary: If you delete a newly-created instance of a set property while editing a Thing, the entire edit can be canceled.
in my SB space:
  1. Edit an existing Event.
  2. Create a new Reference instance. 2a. Change some data in another, unrelated field, such as 'Day'.
  3. Change your mind and click the x button to delete the newly-created Reference.
  4. Note that you are now at the Event display, NOT the Edit screen. 4a. Note also that the data change you made in step 2a seems to have been lost. 4b. Refresh. Note that NOW the data reflects the change made in 2a.