seemingly inconsistent behavior for "kind-indexed" type constraints in GHC 7.6

[Nicolas Frisby]

GHC 7.6 is rejecting some programs that I think ought to be well-typed.

Details here https://gist.github.com/3842579

I find this behavior particularly odd because I can get GHC to deduce
the type equalities in some contexts but not in others. In particular,
it does not deduce them inside of type class instances.

Is this a known issue? I'll create a Trac ticket if that's appropriate.

Thanks for your time.