Attempting to add a release without tracknumbers is impossible. As a kludgy workaround, it is currently possible to make an "Edit medium" which removes the tracknumbers which are automatically added. (note that a hole in the edit system currently allows all tracknumber edits to be autoedits.)
Another example better demonstrating the magical data:
Edit #25991659 is undoing a data change that doesn't have an edit.
I can't imagine how awful it must be that the "Add Medium" and "Edit Medium" code must be maintained separately!