I havent looked at RSS on Twonky in a while myself
But I do remember the problem is even worse than that
They change on restart also
for ex:
Current RSS custom Video Playlist link
http://<server_ip_address>:9000/rss/feed/0$3$73$7490.rss
Server restart RSS same custom Video Playlist link
http://<server_ip_address>:9000/rss/feed/0$3$255$7672.rss
The only ones that dont change are the root ones
Music
http://<server_ip_address>:9000/rss/feed/0$1.rss
Photos
http://<server_ip_address>:9000/rss/feed/0$2.rss
Videos
http://<server_ip_address>:9000/rss/feed/0$3rss
Twonky could do them and all of us a favor if they it created links based off of the actual item name
and generate a link off of some db entry or something like they do now