problems with duplicate modules

Hello, I just noticed the following minor issue. I have a cabal file which isn't seen by cabal except for the configuration step and to install the package, which I do as:

runhaskell Setup.hs -v register --gen-pkg-config=.package-config
ghc-pkg update .package-config --user

If I duplicate a module in the Exposed-modules list then

1. cabal doesn't complain
2. ghc-pkg doesn't complain
3. ghci gives a very misleading message, e.g.:

Could not find module `Vector.Sparse':
  it was found in multiple packages: vectro-0.2 vectro-0.2

Trac metadata

Trac field	Value
Version	6.8.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system	Unknown
Architecture	Unknown