Actually, if we look at it, a PersistentColleciton is already filtered by the owner. When fetch mode is LAZY, we expect it to load it all anyway if we do a $article->getComments() for instance. The only fetch mode where we expect it to be sliced is actually EXTRA_LAZY.

The thing is that if we do it for LAZY, it will usually trigger two queries (the count and the actual requests to fetch the data), which I suppose is not what we want.