When using fastcgi_cache, if the key you are using is too long, say over 255 characters, it appears that fastcgi_cache breaks, and you get errors that look like this:

*18 upstream sent unsupported FastCGI protocol version: 114 while reading upstream,

I've encountered this error in 0.8.54 and 0.9.7

this is an example of a url that will break fast_cgi cache:

http://example.com/wp-admin/load-scripts.php?c=1&load=admin-bar,hoverIntent,common,jquery-color,wp-ajax-response,wp-lists,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-resizable,quicktags,jquery-query,admin-comments,jquery-ui-sortable,postbox,dashboard,thickbox,plugin-install&ver=f8890f4269ea35a6d5e30382070f0a89

using this key:

fastcgi_cache_key $host$request_uri$request_method;

fastcgi backend is php-fpm

system:
Ubuntu 9.04
kernel: 2.6.32.16
arch: i686

Thanks!
Let me know if there is any other info I can provide to help squash this bug!