I am building latest pandoc (1.15.1) on Arch with all dependency being latest. It failed with the following error. 1.15.0.6 builds just fine in the same environment, though.

  53% ( 41 / 77) in 'Text.Pandoc.Readers.Odt.Arrows.Utils'
  Missing documentation for:
    and2 (src/Text/Pandoc/Readers/Odt/Arrows/Utils.hs:51)
    and3 (src/Text/Pandoc/Readers/Odt/Arrows/Utils.hs:54)
    and4 (src/Text/Pandoc/Readers/Odt/Arrows/Utils.hs:57)
    and5 (src/Text/Pandoc/Readers/Odt/Arrows/Utils.hs:60)
    and6 (src/Text/Pandoc/Readers/Odt/Arrows/Utils.hs:63)
    and7 (src/Text/Pandoc/Readers/Odt/Arrows/Utils.hs:66)
    and8 (src/Text/Pandoc/Readers/Odt/Arrows/Utils.hs:69)
    liftA2 (src/Text/Pandoc/Readers/Odt/Arrows/Utils.hs:86)
    liftA3 (src/Text/Pandoc/Readers/Odt/Arrows/Utils.hs:89)
    liftA4 (src/Text/Pandoc/Readers/Odt/Arrows/Utils.hs:92)
    liftA5 (src/Text/Pandoc/Readers/Odt/Arrows/Utils.hs:95)
    liftA6 (src/Text/Pandoc/Readers/Odt/Arrows/Utils.hs:98)
    liftA7 (src/Text/Pandoc/Readers/Odt/Arrows/Utils.hs:101)
    liftA8 (src/Text/Pandoc/Readers/Odt/Arrows/Utils.hs:104)
    liftA (src/Text/Pandoc/Readers/Odt/Arrows/Utils.hs:115)
    ^+++ (src/Text/Pandoc/Readers/Odt/Arrows/Utils.hs:200)
    +++^ (src/Text/Pandoc/Readers/Odt/Arrows/Utils.hs:201)
    ^+++^ (src/Text/Pandoc/Readers/Odt/Arrows/Utils.hs:202)
    ^||| (src/Text/Pandoc/Readers/Odt/Arrows/Utils.hs:210)
    |||^ (src/Text/Pandoc/Readers/Odt/Arrows/Utils.hs:211)
    ^|||^ (src/Text/Pandoc/Readers/Odt/Arrows/Utils.hs:212)
    ^&&& (src/Text/Pandoc/Readers/Odt/Arrows/Utils.hs:220)
    &&&^ (src/Text/Pandoc/Readers/Odt/Arrows/Utils.hs:221)
    ^&&&^ (src/Text/Pandoc/Readers/Odt/Arrows/Utils.hs:222)
    ^*** (src/Text/Pandoc/Readers/Odt/Arrows/Utils.hs:230)
    ***^ (src/Text/Pandoc/Readers/Odt/Arrows/Utils.hs:231)
    ^***^ (src/Text/Pandoc/Readers/Odt/Arrows/Utils.hs:232)
     (src/Text/Pandoc/Readers/Odt/Arrows/Utils.hs:272)
    ReFallibleArrow (src/Text/Pandoc/Readers/Odt/Arrows/Utils.hs:295)
     (src/Text/Pandoc/Readers/Odt/Arrows/Utils.hs:304)
    liftSuccess (src/Text/Pandoc/Readers/Odt/Arrows/Utils.hs:333)
    liftAsSuccess (src/Text/Pandoc/Readers/Odt/Arrows/Utils.hs:339)
    asFallibleArrow (src/Text/Pandoc/Readers/Odt/Arrows/Utils.hs:345)
    >>?haddock: internal error: <stdout>: commitBuffer: invalid argument (invalid character)

Package versions:

Packages (85) haskell-asn1-encoding-0.9.3-1  haskell-asn1-parse-0.9.4-1  haskell-asn1-types-0.3.1-1  haskell-async-2.0.2-1  haskell-attoparsec-0.13.0.1-4
              haskell-blaze-builder-0.4.0.1-1  haskell-byteable-0.1.1-1  haskell-case-insensitive-1.2.0.5-2  haskell-cereal-0.4.1.1-1
              haskell-conduit-1.2.5-1  haskell-connection-0.2.5-1  haskell-cookie-0.4.1.6-1  haskell-cryptonite-0.8-1  haskell-data-default-class-0.0.1-9
              haskell-data-default-instances-base-0.0.1-11  haskell-data-default-instances-containers-0.0.1-9
              haskell-data-default-instances-dlist-0.0.1-10  haskell-data-default-instances-old-locale-0.0.1-9  haskell-digest-0.0.1.2-1
              haskell-dlist-0.7.1.2-1  haskell-enclosed-exceptions-1.0.1.1-1  haskell-exceptions-0.8.0.2-1  haskell-hashable-1.2.3.3-1
              haskell-hourglass-0.2.9-1  haskell-lifted-base-0.2.3.6-1  haskell-memory-0.10-1  haskell-mime-types-0.1.0.6-2  haskell-mmorph-1.0.4-1
              haskell-monad-control-1.0.0.4-1  haskell-old-locale-1.0.0.7-6  haskell-pem-0.2.2-1  haskell-primitive-0.6-3  haskell-regex-base-0.93.2-23
              haskell-regex-pcre-builtin-0.94.4.8.8.35-1  haskell-resourcet-1.1.6-1  haskell-socks-0.5.4-1  haskell-stm-2.4.4-4
              haskell-streaming-commons-0.1.14.2-1  haskell-tls-1.3.3-1  haskell-transformers-base-0.4.4-1  haskell-transformers-compat-0.4.0.4-2
              haskell-unix-compat-0.4.1.4-2  haskell-utf8-string-1-3  haskell-x509-1.6.3-1  haskell-x509-store-1.6.1-1  haskell-x509-system-1.6.1-1
              haskell-x509-validation-1.6.3-1  ghc-7.10.2-1  haskell-aeson-0.10.0.0-2  haskell-base64-bytestring-1.0.0.1-4  haskell-blaze-html-0.8.1.1-2
              haskell-blaze-markup-0.7.0.3-1  haskell-cmark-0.4.1-1  haskell-data-default-0.5.3-10  haskell-deepseq-generics-0.1.1.2-1
              haskell-extensible-exceptions-0.1.1.4-12  haskell-filemanip-0.3.6.3-3  haskell-haddock-library-1.2.1-1  haskell-highlighting-kate-0.6-3
              haskell-hslua-0.4.1-1  haskell-http-4000.2.20-4  haskell-http-client-0.4.24-2  haskell-http-client-tls-0.2.2-2  haskell-http-types-0.9-2
              haskell-juicypixels-3.2.6.1-1  haskell-mtl-2.2.1-4  haskell-network-2.6.2.1-3  haskell-network-uri-2.6.0.3-1  haskell-old-time-1.1.0.3-6
              haskell-pandoc-types-1.12.4.7-3  haskell-parsec-3.1.9-5  haskell-random-1.1-4  haskell-scientific-0.3.4.2-1  haskell-sha-1.6.4.2-3
              haskell-syb-0.6-2  haskell-tagsoup-0.13.3-1  haskell-temporary-1.2.0.3-1  haskell-texmath-0.8.4-1  haskell-text-1.2.1.3-3
              haskell-unordered-containers-0.2.5.1-2  haskell-vector-0.11.0.0-3  haskell-xml-1.3.14-1  haskell-yaml-0.8.15.1-3
              haskell-zip-archive-0.2.3.7-1  haskell-zlib-0.6.1.1-1

I don't know if it's a problem in haddock or pandoc, or even in my build environment. Would like some suggestions, many thanks!

$ haddock --version
Haddock version 2.16.1, (c) Simon Marlow 2006
Ported to use the GHC API by David Waern 2006-2008

Hrm, strange :/

I just figured out the problem - it only fails with locale setting to "C". The last version 1.15.0.6 didn't have the issue though, so this is probably related to this commit: 82b3e0a

By specifying LC_CTYPE=en_US.UTF-8 for runhaskell Setup haddock --hoogle --html the problem no longer occurs.