Hi again,

On the same website 'hungry happens .com", the search module on the sidebar brings always the same results.
I have cache off on the module , and of course on, on the joomla.
Same issue exactly with the tags : www.hungryhappens.com/Subjects/recipes.html
No matter which tag you click gives the same results. I had to completely disable system cache, but this is not an option since the site is getting hundreds of thousands visitors on a daily basis.

Help is needed, thanks in advance

Are you using an SEO/SEF extension or K2's advanced SEF?

I'm using SH404, but what this have to do with the search/tag cache?

Sh404 rewrites all URLs and handles all redirects.
If sh404 results are not cached properly then you will most definitely face some issues. Same thing applies to the K2 system plugin.

You have to make sure that the caching system plugin is rendering after these plugins.

Finally you might find some usefull resources about SH404 and caching issues at their site.

My guess is the plugin order.

Right now I have SH404 on, and I just have disable system cache and everything working.
I can see that SH404 cache is also working and there is no issue.

Ok, This means that this is a system cache issue.

Apart from not caching these modules did you check the plugin order?