Override the attributes plugin and 'fix' it to perform proper inheritance. There is not going to be an official fix as the behavior is deemed by design, which I found out when filing
issue #358 CanJS.
(In my honest opinion; having no way to 'untype' an attribute is a
very weak reason to break the principle of least surprise in this way, but if that's the way the developers want to move forward; so be it. I'll just happily keep monkey-patching sane behavior back in..)