Yeah I've noticed that.  I tried debugging the problem but I ended up with the conclusion that it was something with Epic's code.  I'm not sure if it's server side or client side (more likely client side).  It seams kind of random, I compiled the gun on UT3 1.1 Beta 1 and played on that version and only saw it on DM-Diesel.  I asked around and I was the only one who saw the problem.  I've since got a new computer and reinstalled UT3 and havn't had the problem.  I'm running patch 1.1 on both my client and the server.