Backpack doesn't check for fixity consistency

This should fail, but instead it prints 7.

unit p where
    signature A where
        infixl 6 `mul`
        infixl 7 `plu`
        mul :: Int -> Int -> Int
        plu :: Int -> Int -> Int
    module P where
        import A
        x = 2 `mul` 3 `plu` 1
unit i where
    module A where
        infixl 7 `mul`
        infixl 6 `plu`
        mul :: Int -> Int -> Int
        mul x y = x * y
        plu :: Int -> Int -> Int
        plu x y = x + y
unit main where
    dependency p[A=i:A]
    module Main where
        import P
        main = print x

Trac metadata

Trac field	Value
Version	8.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Type checker)
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture