I have noticed a weird behaviour as some of the out of stock products display when using size filters, for example when I go to t-shirts category and specify a brand and a size I can see 5 t-shirts, but only 3 of them are available in the correct size. I checked the products and for both it says that the quality is 0 and stock availability is 'out of stock' which seems to be as expected. I made sure that the cache is clear and all the indexes are updated.
So I wonder if anyone faced this problem before and how can it be solved?