Images with transparent background?

Hi,

I am trying KdenLive for the first time, it seems quite nice and I started a project.

In this project I edited a image to get a transparent background (with the grey squares) and exported it to png(tried other formats too).
Then I imported it to the clips (with the transparent background cheked), but when I put it into the timeline on the top track it shows a black background and not the track bellow as I expected (sometimes a white background when I did experiences with gimp).

Anyone knows want I am doing wrong?

Thanks.