Firstly, a very popular (nearly 1500 seeds) torrent was found. I added it to KTorrent with uTP disabled and all worked well, download speed was good.
After this, I enabled "Use uTP" and "Only use uTP" and restarted KTorrent. Download speed was zero, there was no peers in peer list.
Finally, I launched uTorrent under Wine. uTP worked well here.
I did this steps several times. Sometimes uTP in KTorrent works well, sometimes doesn't work at all. As I noticed, if I'm not restarting KTorrent after changing settings there is a greater chance to see uTP working.
If uTP doesn't work and there is no peers in peer list, I can notice a "failure" near "Authenticate" and "Initiating connection" lines.
P.S. KTorrent version is 4.1

Haven't seen any problems with µTP lately, send me the torrent or link to a torrent. So I can reproduce it.

It doesn't depend on torrent.
Try this: http://vodo.net/media/torrents/Sintel.2 ... DO.torrent
Yes, really, if I'm restarting KTorrent after turning up "uTP only" there is no connected peers at all, but if I'm NOT restarting all works well. If I'm turning both TCP and uTP and restarting KTorrent only TCP works.
Also uTP consumes much more CPU time. 30 torrents seeded without uTP consumes 1, rarely 2 procents of CPU time. 2 torrents with uTP enabled (also seeding) consumes 5-7%, sometimes 9.

Everything seems to be working with µTP only and that torrent.

Is encryption enabled ?

George wrote:Is encryption enabled ?

Both encrypted and unencrypted connections are enabled.