GHC (without -XBangPatterns) silently accepts bang patterns in outermost position

GHC 6.8, 6.12, 7.0 at least accept bang patterns on the outside of patterns silently.

main = do
    let !x = 1
    return ()

I expect an "illegal bang pattern" error, but it is accepted:

$ ghci A.hs
GHCi, version 7.0.0.20101028: http://www.haskell.org/ghc/  :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
Loading package ffi-1.0 ... linking ... done.
[1 of 1] Compiling Main             ( A.hs, interpreted )
Ok, modules loaded: Main.

However, if we move it inside some parens, it correctly fails:

main = do
    let (!x) = 1
    return ()

failing with

A.hs:2:10:
    Illegal bang-pattern (use -XBangPatterns):
    ! x

Trac metadata

Trac field	Value
Version	7.0.1 RC1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Parser)
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