I wrote:
> What I would have expected to happen is for the ALTER TABLE to throw an
> error telling you it couldn't cope with updating the rule, and that
> you'd need to fix that manually. There is such a test involving views;
> not sure why it's not catching this rule.
FYI, I've committed a patch that will cause 9.2 and later releases to
report an error for this case.
regards, tom lane