Yeah -- single units should be compared by identity.  The "hour" that is "built-in" to astropy should be considered different from an "hour" that the user creates.  Identity is the only thing we have to ensure the uniqueness of base units.

That said, this PR didn't create the problem, but it has crept in elsewhere at some point due to the test suite not being good enough on this point.  I'll try to work up a PR to fix that...