The standard should simply be changed to throw by default, but I guess the train has already left the station and so we're left with "bugs by design" before the spec has even been fully implemented by all vendors :(

But then again, in it's current "minimal" state of design, the Harmony Promises are inferior to any of the dedicated Promise A Plus implementations out there (e.g. Bluebird) and at least under Node there is little to no reason to use the built-in Promise object at this point in time.