As Conal reported on the mailing list[1], ghc-pkg check on Mavericks allegedly returns:

bash-3.2$ ghc-pkg check
    Warning: haddock-interfaces: /Users/conal/.cabal/share/doc/x86_64-osx-ghc-7.8.1/uniplate-1.6.12/html/uniplate.haddock doesn't exist or isn't a file
    Warning: haddock-interfaces: /Users/conal/.cabal/share/doc/x86_64-osx-ghc-7.8.1/polyparse-1.9/html/polyparse.haddock doesn't exist or isn't a file
    Warning: haddock-interfaces: /Users/conal/.cabal/share/doc/x86_64-osx-ghc-7.8.1/ghc-syb-utils-0.2.1.2/html/ghc-syb-utils.haddock doesn't exist or isn't a file
    Warning: haddock-interfaces: /Users/conal/.cabal/share/doc/x86_64-osx-ghc-7.8.1/constraints-0.3.5/html/constraints.haddock doesn't exist or isn't a file
    Warning: haddock-html: /Users/conal/.cabal/share/doc/x86_64-osx-ghc-7.8.1/constraints-0.3.5/html doesn't exist or isn't a directory
    Warning: haddock-interfaces: /Users/conal/.cabal/share/doc/x86_64-osx-ghc-7.8.1/newtype-0.2/html/newtype.haddock doesn't exist or isn't a file
    Warning: haddock-html: /Users/conal/.cabal/share/doc/x86_64-osx-ghc-7.8.1/newtype-0.2/html doesn't exist or isn't a directory

It's not fatal, but makes the output much more annoying. I figured this would have been caught by validate or somesuch, but apparently not.

Marking for 7.8.2. I'm looking into this soon.

[1]http://www.haskell.org/pipermail/glasgow-haskell-users/2014-April/024846.html