I have two videos - one in each track. The video in the upper track is cut so for some seconds it reveals the lower one. No transitions is used. However, when revealing the lower layer it stutters. Adding a very short (3- frames) fade transition prevents the stutter. If I hide/mute the upper track it also does not stutter. This happens in the timeline as well in the rendered result.
I made a short demonstration of the problem here: http://youtu.be/8Fz98KjndH0
Ubuntu 12.04 (beta 2)
Kdenlive Version 0.8.2.1 Using KDE Development Platform 4.8.1 (4.8.1)
I tried with the git version from ppa as well. Same result.