rendering crashing with title clips

Hello,

I am using Kdenlive Version 0.9.2. and Ubuntu 12.10.
I have been using Kdenlive for a week to cut videos and render them into .mp4 files. Until today, I haven't encountered any problem. But today, as I tried to render a project including a title clip with a slide transition, the rendering unfortunately crashed. After trying several things, I have come up to think that the problem arises with the title clip whatever the profile is. Everything is ok when my project don't have any title clip.

Here is the message I got when the file crashed :

Rendering of /home/*/kdenlive/untitled.mpg crashed
[mpeg @ 0x7fd1d00c6ae0] VBV buffer size not set, muxing may fail
melt: /build/buildd/libav-extra-0.8.4ubuntu0.12.10.1/libav/libavcodec/ratecontrol.c:693: ff_rate_estimate_qscale: Assertion `picture_numbernum_entries' failed.

Last but not least, I get a message of "internal error" from Ubuntu everytime I try rendering a file with a title clip.

thank you very much for your help