With the release 2.9.1 Issue #6659 was introduced: Return HTTP 204 instead of GIF for JavaScript tracking.
Has this been well-thought-out? The proxy script doesn’t take this into account IMO.
Now I have an entry in my PHP error log for every piwik request because [function.file-get-contents]:
failed to open stream: HTTP request failed! HTTP/1.1 204 No Response
in piwik.php on line 75
I have fixed the problem you reported, could you give it a try and confirm it is indeed fixed? You should download the new piwik.php (proxy) from here: https://github.com/piwik/tracker-proxy
We have PHP 5.4 installed, still piwik.php returns 204 no response, because of this our application sometimes gets stalled or it takes as long as 5 min to completely load the page.