Restore deleted menu items

It was always previously possible to "undelete" a deleted menu item by "re-deleting" it. See Inga's article:

But now it seems this isn't possible. I have an interface with the File > New... deleted (& replaced with a custom VB tool to create files to company naming standards). However, if I try to restore the menu item, delete is not active.

Am I missing something?

(I can work around the problem by exporting the interface XML, removing the <UserDeleteMenuEntry> entry and reimporting into a new dgnlib, but it would be nice to know why it can't be done through the interface.)