Wish I could help more, but am on 10.2.8. Anyway, I was getting some problems with iTunes support since the new iTunes 4.1 wanted port 3689 also open. So I added that to the firewall and router.

Try disabling the iTunes support for a download or two to see if the problem is in the saving/verification. Another idea would be to look at the "disable ultrapeer" checkbox in the prefs. If your set-up has trouble handling 60-some host connections as an Ultrapeer, that might seem to lock things up.

Just some ideas--hope a user with 10.1.5 might have better ones.