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

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.