Incorrect warning about redundant constraints

The following program results in an incorrect warning about a redundant constraint:

{-# LANGUAGE TypeFamilies #-}

type family SomeFun a 

f :: (SomeFun i ~ [a], Read a) => proxy i -> a
f _ = read "HELLO"

This is the warning:

Redundant constraint: SomeFun i ~ [a]
    In the type signature for:
         f :: (SomeFun i ~ [a], Read a) => proxy i -> a

I tried it on GHC version 7.11.20151029

Trac metadata

Trac field	Value
Version	7.11
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Type checker)
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