After rendering (with youtube profile if it matters), my title clips show up as a screen-filling string "Invalid" in mplayer.
I'm using today's svn/git versions of ffmpeg, mlt and kdenlive.

(Kdenlive rev. 3615,
mlt commit 0cd7a3adb4169bb37f8dee073205454db9a5648b Author: Dan Dennedy Date: Fri Jun 19 22:30:50 2009 -0700
ffmpeg rev. 19244)

Thank you for pointing me to the other thread. I will add some comments there as there's no use in having two threads about the same.