unindent not correctly recognized (possibly in connection with `infix`)

[andreasabel]

The following code is indented incorrectly:

  showInverse x = do
      q <- invert x
      return $ show q
    `catchError` \ e -> return "infinity"

It's rendered more like this:

  showInverse x = do
    q <- invert x
    return $ show q
     `catchError` \ e -> return "infinity"

(and that has a different meaning in Haskell).