Broken javascript after proxy

I'm using google's gwt-gadgets library in gadget development. Generated javascript may contain construction like this:

$replace(SQUOT_RE, s, ''')

When this javascript is going thru proxy, it gets broken

$replace(SQUOT_RE, s, ''') // 3 apostrophes

The script is served as "text/javascript" content type.

What helped for me is disabling content modification in php/src/gadgets/MakeRequest.php line 119:

  && strpos($result->getContentType(), 'javascript') == false) {