We don't usually *break* existing working code even if the output is wrong.  If you want to make '%x' % 3.14, etc, raise an error, I think you we should go through a deprecation period first.  The deprecation messages should, of course, be added now.

In other words, I would probably have voted against commit even if we weren't in beta yet.  It's a bit borderline, since the output is *wrong*, but given that we *are* in beta I think we'd better go the deprecation route.