Deriving in associated data families ignores instance's constraints

This code

class Class a where
  data DF a

data family DF' a

instance (Eq (DF' a)) => Class a where
  newtype DF a = DF (DF' a) deriving (Eq)

fails with

No instance for (Eq (DF' a))
    arising from the 'deriving' clause of a data type declaration
  Possible fix:
    add an instance declaration for (Eq (DF' a))
    or use a standalone 'deriving instance' declaration,
         so you can specify the instance context yourself
  When deriving the instance for (Eq (DF a))

The following way it compiles fine, however

class Class a where
  data DF a

data family DF' a

instance Class a where
  newtype DF a = DF (DF' a)

deriving instance (Eq (DF' a)) => Eq (DF a)

Trac metadata

Trac field	Value
Version	7.6.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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