I just experienced an issue with comparing products in the ecom product catalog.
In a template we are using some "continuous scroll"-like thingie, which keeps appending the following pages on a product list using ajax (replacing the standard pagination links).
The template also contains functionality for product comparison, where we mark the products we want to compare - and these products might be on different pages (PageNum) of the product list.
The comparison page (?Compare=...) didn't work as expected. Apparently, it couldn't compare products that was located on different pages in the product list. We could only compare products that was on the same product list page (e.g. PageNum=2).
However, when we disabled the "Enable optimized product retrieval" everything worked fine. We can now compare products across pages.
Is this a bug or "by design"? :)