Dear Adriano
I did some more testing today and found what is causing the problem.
1. First to say that I had two colleagues with different IP addresses log-in to the website and then use the front end filters at http://audio-gear.org/products-for-sale/
In each case the problem is visible; i.e. clicking on a filter does refresh the screen but does not filter the results.
2. Next I began to reconstruct the View 'Product Listing 3' section by section. The filters worked fine until I reinserted the CRED form 'Add to Cart'. As soon as I inserted this CRED form then the filters stopped working again. I tried this a number of times and it was consistent.
3. Then I tried replacing the CRED form 'Add to Cart' with another CRED form. The filter problem remains.
So in summary, it seems that the inclusion of any CRED form within the view is causing the front end filter operation to fail when it is set to 'Update the View results every time an input changes' This also explains why there is no problem with the filter operation on my home page which uses a view containing no CRED forms.
I hope this might help to find a solution.
Regards
Robert