For some reason, filetransfers here only use IBB:
On sending side, I see 1) an outgoing feature negotiation/StreamInitiation packet (both IBB and Bytestreams featured there), 2) an incoming ack packet (again featuring IBB and Bytestreams), 3) an outgoing open ibb/IBBExtensions$Open packet (?!).
Why doesn’'t get Bytestreams a chance?