PS 1.5.2 - weird url problem when navigating through categories

[marhor.hr]

Lately I'm having complaints from customers about broken links when they navigate through categories in my shop.

 

I'm using PS 1.5.2. Theme is customized (css and a little bit of layout), using default theme as starting point.

Friendly URL is activated. Although backoffice sais that mod_rewrite is not active or cannot be checked, hosting provider assures me that mod_rewrite is active.

 

What's happening is that navigating through categorys functions normaly for some time - the url which is shown in browser status bar if hovered over the category link looks normal, like this:

   "mydomain/id-categoryname"

 

After browsing for some time, the url becomes messed up and looks like this:

     "mydomain/id-categoryname/&??=&selected_filters=&??=&selected_filters=&=&??=&p=13"

When clicking, the 404 error page opens up.

 

This is because when the url becomes messed up, the last "&p=13" part is random - it can be like "p=2" or "p=3", etc. I suppose that "p" stands for page number. Default number of products shown per page is 9. So if the category I wan't to open has for instance 12 products, there will be 2 pages. But in mentioned case, the wrongly generated url tries to open the 13th page and visitor sees the 404 error page.

 

Also, sometimes the broken url looks like this:

"mydomain/id-categoryname/štapovi-za-hodanje.jpg"

 

Now, I have no clue why is this image name appended to the url. Off course such page does not exist in the shop and visitors sees the 404 page again.

 

As for other seo& url options, I have tried all combinations of "friendly URL", "Automatically redirect to Canonical URL", "Disable apache multiviews", but it helps only if friendly url is disabled.

 

I have also replicated the shop on another domain (replicated files and database, different domain name, different hosting provider), trying to replicate the problem there, but was unable to do it - this site seems to work normally, at least for the time being.

 

Needless to say, i'm completely lost. Any help, insight, advice is greatly appreciated.

 

Thanks!

Edited January 15, 2014 by marhor.hr (see edit history)