Warnings on record updates

When I compile the following module with the -Wall option on ghc v6.2.1  
I get warnings:
Warning: Pattern match(es) are non-exhaustive
    In a record-update construct: Patterns not matched D2.
The warnings occur at both of the indicated places in the module.
Since the functions both handle all the cases of the data type D, it  
seems the warning should not be given.

------------------------------------------------------------------------ 
---------

module Try where

data D = D1 { f1 :: Int } | D2

-- Use pattern matching in the argument
f :: D -> D
f  d1@(D1 {f1 = n}) = d1 { f1 = f1 d1 + 1 } -- Warning here
f  d = d

-- Use case pattern matching
g :: D -> D
g  d1 = case d1 of
          D1 { f1 = n } -> d1 { f1 = n + 1 } -- Warning here also
          D2            -> d1

Cheers

Peter White
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