Since enabling the fastcgi_cache on my nginx server, my php-enabled custom error page has suddenly stopped working and I'm getting the internal 404 message instead.

In nginx.conf:

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;

map $uri $no_cache_dirs {
   default 0;
   ~^/(?:phpMyAdmin|rather|poll|webmail|skewed|blogs|galleries|pixcache) 1;
}

the cache relevant stuff in my fastcgi.conf:

fastcgi_cache MYCACHE;
fastcgi_keep_conn on;
fastcgi_cache_bypass $no_cache $no_cache_dirs;
fastcgi_no_cache $no_cache $no_cache_dirs;
fastcgi_cache_valid 200 301 5m;
fastcgi_cache_valid 302 5m;
fastcgi_cache_valid 404 1m;
fastcgi_cache_use_stale error timeout invalid_header updating http_500;
fastcgi_ignore_headers Cache-Control Expires;
expires epoch;
fastcgi_cache_lock on;

If I disable the fastcgi_cache, the php-enabled 404 page works as it has for years.

How would I disable the cache for the custom error page?