Since upgrading from 2.1.4 to 2.1.6 i'm getting the following error in my error logs :

PHP Fatal error: Uncaught exception 'RuntimeException' with message 'The Expires HTTP header is not parseable (-1).' in /var/www/releases/20121221154853/app/cache/prod/classes.php:2576"

I'm using the httpcache with esi enabled and have upgraded my views to use the render url method.
Disabling the appcache removes the error.

Because of the security issue I cannot go back to 2.1.4 and so have disabled the http cache for now.

I've found the same error in this pull request #6037, which was added to symfony between 2.1.4 and 2.1.6 but doesn't mention a needed change to the code.

My app is used by Internet Explorer 6 and up, so maybe that has something to do with the '-1' in the header. Requests with http 1.0 now fail. This is easily reproducable by using curl -0 http://websiteurl.

Any help would be appreciated