When type classes are redefined in GHCi bindings that use old instances are still accessible

I found the following behavior surprising:

GHCi, version 8.0.1: http://www.haskell.org/ghc/  :? for help
Loaded GHCi configuration from /tmp/ghci7261/ghci-script
Prelude> class Foo a where { foo :: a -> Int }
Prelude> instance Foo () where { foo _ = 1 }
Prelude> f = foo ()
Prelude> class Foo a where { foo :: a -> IO () }
Prelude> f
1

Foo is redefined but f which uses a now illegal instance of Foo is still accessible. I would have expected that any bindings that use the old foo (or have the old foo in their call graph) would be cleared.

Trac metadata

Trac field	Value
Version	8.0.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	GHCi
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