Looking at the changelog doesn't really give a clue as to why this started happening again, but here goes: RC 5 seems to have reintroduced a problem with uTP while uploading. When seeding at a high speed the connection will rapidly slow down when a peer using uTP connects. This happened with 1.8.x but was fixed in RC 3 and RC 4. Changing bt.transp_disposition from the default 15 to 5 fixes the problem, but I thought you'd like to know anyway.