A minimal example that showcases Cabal bug #4253
$ cabal install package1/ package2/
$ ghci -XPackageImports
GHCi, version 8.0.2: http://www.haskell.org/ghc/ :? for help
Loaded GHCi configuration from /home/rgscott/.ghci
λ> import "package1" DuplicateModuleName
λ> Window
<interactive>:1:1: error:
Ambiguous interface for ‘DuplicateModuleName’:
it was found in multiple packages:
package1-0.1.0.0 package2-0.1.0.0