Sorry for that i did not noticed this soon enough, but there is a problem on HDbits tracker with KTorrent's user-agent.
A member told us on their forum that KIO enabled did backfired, this is what he told:

hmm, KIO mode seams to be problematic, if i disable it, all works fine but when i enable it i get "banned client" once again :-/ strange, because 3.3.2 worked with KIO enabled for long time just fine.

Just so you know