The GHC parser (in Haddock mode) failed:
  benchmark/weigh-pandoc.hs:14:1-6
  parse error on input `import'

Formatting is not idempotent:
  src/Text/Pandoc/Readers/Vimwiki.hs<rendered>:613:19
  before: ".softbreak <$ endlin"
  after:  ".softbreak\n    <$ en"
Please, consider reporting the bug.