mod_proxy uses its own routine named 'send_dir' in proxy_ftp.c to output
the contents in ftp directories. Unfortunately this routine doesn't update
the amount of bytes written so that subsequent requests for the same 
directory will result in a directory listing with "Content-Length: 0".

The patch to fix this bug below applies on top of the patch given in bug
report 10747:

--- proxy_ftp.c.orig    Fri Jul 12 18:19:04 2002
+++ proxy_ftp.c Fri Jul 12 22:31:31 2002
@@ -1358,7 +1359,7 @@
             ap_proxy_send_fb(data, r, c, -1, 0, 0, conf->io_buffer_size);
         }
         else {
-            send_dir(data, r, c, cwd);
+            c->written=send_dir(data, r, c, cwd);
         }
         /* ap_proxy_send_fb() closes the socket */
         data = NULL;