[franze]

here the problem comes in, as people write

  User-agent: googlebot
  User-agent: bing    #behaved-badly
  User-agent: yandex
  Disallow: /

if # removes everythin afer the #, then it would be

  User-agent: googlebot
  User-agent: bing    User-agent: yandex
  Disallow: /

which results into the whole line " User-agent: bing User-agent: yandex" beeing thrown out as malformed, so only googlebot would be disallowed.