Not sure what is in the platform as I just did the following:
cabal install -j3 haddock
Resolving dependencies...
Configuring ghc-paths-0.1.0.9...
Configuring haddock-library-1.2.0...
Building haddock-library-1.2.0...
Building ghc-paths-0.1.0.9...
Installed ghc-paths-0.1.0.9
Installed haddock-library-1.2.0
Configuring haddock-api-2.16.0...
Building haddock-api-2.16.0...
Installed haddock-api-2.16.0
Configuring haddock-2.16.0...
Building haddock-2.16.0...
Installed haddock-2.16.0
Updating documentation index
/Users/gcolpitts/Library/Haskell/share/doc/x86_64-osx-ghc-7.10.1.20150601/index.html
If nobody else is seeing the problem I did, I don't think we should worry about it.