I'm using Kdenlive for about half a year now, haven't had major problems at all. A few days ago I updated my Gentoo-system to ~x86, which is the "unstable" branch of portage. From all I heard and looking at the other programs running fine, this "unstable" branch isn't very unstable.
With this update, Kdenlive was updated from 0.9.2. to 0.9.4 and mlt from 0.8.2 to 0.8.8. Now, when I try editing a video, the audio is out of sync with the video and stutters. A lot. I have a video-track without audio, an audio-track containing the videos audio and a second audio track. The project was generated with the old version of Kdenlive and all was fine. When I opened the project in the new version, the audio is out of sync, I think. Can't really tell, because of the stuttering, but I think it's a bit of. Also, when I try to render a part of the project, after about 2 minutes, my 8 GB Ram is full. That didn't happen before. I tested this with a part of the project I could successfully render before.
After playing around with audio-/video-drivers and opengl (and disabling pulseaudio via pasuspender), I gave up and decided to downgrade - which didn't make Kdenlive usable again. After downgrading back to 0.9.2 (mlt: 0.8.2) the audio and video is really badly out of sync. Not only in the preview, but also after rendering. Funny thing: I chopped the audio-tracks at their beginning and kdenlive does play the chopped part, which it shouldn't. Oh, and when i seek through the playing preview, the sound just continues playing like i wasn't seeking, while the video jumps to the correct position.
By the way: I tried using melt (both versions) to play videos, it worked like a charm.
Some more information about my system: 8 GB Ram, 3,2Ghz Quadcore (Intel i5), 2 graphic-cards (both nvidia, one GeForce GTX 295, one Quadro FX 580), using Gentoo (last synced: two days ago or so), using pulseaudio, but tried starting Kdenlive with pasuspender.
As you probably can imagine, i can't use Kdenlive like this. I really hope, someone can help me.