partial purge with ngx_http_slice_module returns 404

[infinityhacks]

slice              1m;
proxy_cache_key    $host$uri$is_args$args$slice_range;
proxy_set_header   Range $slice_range;

After several test, I found when the proxy_cache_key ends with $slice_range which is a key config of ngx_http_slice_module, the partial purge will return 404.

The partial purge can work after I remove $slice_range from the cache key.

With my test, the purge_all function can work well under this situation.