No, this does not work that way. If you have A.i386 and A.x86_64
installed, and they do have common files, then an attempt to update
only one from this pair ends up with conflicts. Seth already
suggested that yum may have a "pair check" which woud allow either
both updates or none.
Could I persuade you to open a bug about the above so I don't forget to
look at it?
Thanks.
-sv