md5 fastcgi cache collisions

[Ian M. Evans]

Was looking at my error log and noticed a whole bunch of errors like this:

2012/09/22 15:52:26 [crit] 641#0: *4896016 cache file
"/var/lib/nginx/fastcgicache/3/21/32d5a44032aadeeed2b1d027314ba213" has
md5 collision, client: x.x.x.x, server: www.example.com, request: "GET
/cr/denzelwashington/ HTTP/1.1", host: "www.example.com"

My fastcgi cache is setup as follows:

fastcgi_cache_path /var/lib/nginx/fastcgicache levels=1:2
keys_zone=MYCACHE:5m inactive=2h max_size=1g loader_files=1000
loader_threshold=2000;
map $http_cookie $no_cache { default 0; ~SESS 1; }
fastcgi_cache_key "$scheme$request_method$host$request_uri";
add_header X-My-Cache $upstream_cache_status;

/cr is actually a php file called like this in the nginx.conf from a
thread years ago:

location ~ ^/cr(/.*$|$) {
rewrite ^/cr(/.*$|$) /$1.php?mypath=$2 last;
}

Site's working fine...just wondering what's causing all the collisions.

Thanks.