kdenlive: problem with a transation
 

I'm a rookie and this is my first attemp to create something with kdenlive.

I want to "present" the clip the viewer will see. So I created a text clip (with a black background... I think) with the title at the botton right corner. I also created a png with the first photogram of the clip. They both last 5 seconds.

I placed the png in track 0, I placed the text on track 1, created a crossfade transition and it works! I see first the title of the clip, it fades out and the png fades in. That lasts 5 seconds. Cool!

Then, on track 0 after the png I placed the real clip which lasts over 1 minute. But when I see the timeline monitor, the clip is displayd completely blank, and it remains so even when exporting. What am I doing wrong?