Here is a complaint about single-port Prolific PL2303 adapters, with which I've experienced reliability issues (note I meant to say "Prolific" not "PLX" in previous comment; PLX makes perfectly good PCI bridges, not cheap USB chips). It makes the observation about dropped bytes, but doesn't have an explanation about why they are prone to occasional data loss; I think that was in a forum post not a mailing list post, and I still can't find it.
If your problem is instead a more generic 2.0 hub driver problem, could you post a link discussing it? With details, I might be able to go check commit messages to see if it has supposedly been fixed.