Weird caching error

Using memcached/dalli on rails 2.3.5

I am trying to render to partials from the cache..and I see the
following messages in the production log.

[DEBUG 17-09-2010 10:03:06] Cache read: category_nav
[DEBUG 17-09-2010 10:03:06] 127.0.0.1:11211 running memcached v1.4.2
[DEBUG 17-09-2010 10:03:06] Cache hit: category_nav ({})
[DEBUG 17-09-2010 10:03:06] Rendered shared/_cat_nav_list (4.0ms)
[DEBUG 17-09-2010 10:03:06] Cache read: city_nav
[DEBUG 17-09-2010 10:03:06] Cache hit: city_nav ({})

I can read both category_nav and city_nav partials from the production
irb console and see the desired html output.

How ever they don't render in the page!

This is what I do in the partials

<% Rails.cache.fetch 'category_nav' do %>
<!-- html content -->
<%end%>

Why is this happening? Also, whats the empty hash in [DEBUG 17-09-2010
10:03:06] Cache hit: category_nav ({}) <= this one.

Thanks