Space leak Control.Monad.Strict

I wrote some code depending on Control.Monad.State.Strict, with the assumption that it would run in constant space. This assumption was wrong. Why? I included a runnable example.

import Control.Monad.State.Strict

data Foo = Foo !Int !Int deriving Show

foo = flip runState (Foo 1 2) 
           (forever $ 
               Control.Monad.State.Strict.modify (\(Foo a b) -> Foo a (b+1))      
           )
main = putStrLn (show foo)

I labeled it "critical", since not being able to use the State monad is making the code less expressive.

Trac metadata

Trac field	Value
Version	6.7
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
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Operating system	Unknown
Architecture	Unknown