nested get_cache

Following this advise I'm trying to do a nested get_cache.

http://lists.danga.com/pipermail/memcached/2007-July/004581.html

Forum.get_cache(185).users works fine and gives me back a list of users
however these users don't have the associations I'm looking for so I'd
like to do another lookup like this

User.get_cache(Forum.get_cache(185).users) or
User.get_caches(Forum.get_cache(185).users)

When I look at the query however this is what I see

...WHERE (`users`.`id` IN (0,0,0,0,0,0,0,0,0))

Do I need to do some type of flatten ?

Help please!