I was adding some URLs from my phone (an Android phone using Mobile Safari 533.1 apparently).

When I paste http://m.youtube.com/#/user/ogachannelofficial?&desktop_uri=%2Fuser%2Fogachannelofficial it turns into http://www.youtube.com/#/user/ogachannelofficiall (note the extra l at the end)
When I paste http://m.youtube.com/#/user/ogachannelofficial? it turns into http://www.youtube.com/#/user/ogachannelofficia
When I paste http://m.youtube.com/#/user/ogachannelofficial it turns into http://www.youtube.com/#/user/ogachannelofficlia

I can't reproduce it on a desktop browser nor in Opera or Firefox on my phone, nor if I edit the URL (so that it doesn't trigger the cleanup), paste it and then fix the URL (so that the cleanup is triggered) so it looks like the combination of pasting and cleaning up the URL at the same time is the problem.