new workbooks, presumably.
Confirmed

gnumeric_dialog_run doesn't return for result_id's >= 0. "Discard all" has
result_id = -GTK_RESPONSE_NO = +9.

And SaveAll is -GTK_RESPONSE_YES.
Strange -- this obviously used to work.

Not strange. Jody changed gnumeric_dialog_run like this.

-	result = gtk_dialog_run (dialog);
+	while ((result = gtk_dialog_run (dialog)) >= 0)
+	       ;

in order to use it for prev/next buttons in druids (like stf). But it is wong to
  assumpe that a user defined response_id should never destroy the dialog.

The solution altenatives are:
- reserve a range of response_ids for druidic behaviour.
- not use gnumeric_dialog_run both for druids and normal dialogs.

I'd go for just defining

GNM_DRUID_NEXT = 1000
GNM_DRUID_PREV = 1001

and loop on those only.

Fixed by changing respons ids for "discard all" and "save all" to
GNM_RESPONSE_SAVE_ALL / GNM_RESPONSE_DISCARD_ALL. These are < 0, and work with
current gnumeric_dialog_run.