Here some information here [1]. It seems thaht there is a bug report here [2]. The fix was pushed by Richard Eisenberg around 2013 here the commit number in the haddock repository 9f356e8b53b3770293c8fd4e91fe1a2b40e42dee [1] https://mail.haskell.org/pipermail/ghc-devs/2013-July/001766.html [2] http://trac.haskell.org/haddock/ticket/242