This is an archived snapshot of W3C's public bugzilla bug tracker, decommissioned in April 2019. Please see the home page for more details.
The spec just says: "Setting the value attribute must set value to the new value." I think it should say: "Setting the value attribute must [change] value to the new value." -- where [change] links to http://dom.spec.whatwg.org/#concept-element-attributes-change
Fwiw, WebKit, Blink, and Gecko all get this right (delivering an attribute mutation).
https://github.com/whatwg/dom/commit/fba1d990d903253b4686dbcbd3f1740d42bddbb3