cannot do screenshots with png

I am trying to get some screenshots of my desktop using

cvlc -vvvv -I dummy --x11-display :0.0 screen:// --video-filter scene -V dummy --scene-ratio 10 --scene-format png --scene-prefix img --scene-path /home/alin --no-scene-replace --run-time 1.5 vlc://quit >png.log 2>&1

however the png files I get seem to have a corrupted header... at least this is what imagemagick tells me... If I change to jpg everything is as expected, I get my frames.

I use vlc 2.0.5... I have also added the log. I have tested both on opensuse 12.3 libpng15 and some newer version libpng16.