Post any defects you find in the released or beta versions of the ImageMagick software here. Include the ImageMagick version, OS, and any command-line required to reproduce the problem. Got a patch for a bug? Post it here.
I've tried this command on my computer at work with Ubuntu 12.10 and ImageMagick version 6.8.0-4.
Now I've tried it again at my home computer with Ubuntu 12.10 and the same ImageMagick version and the image is ok.
I found out, that I've got a self-compiled ImageMagick version at home, because the original version on Ubuntu 12.10 is 6.7.7.
I've compiled the newest ImageMagick version 6.8.2-3 on my work computer and the image looks good.
For the sake of completeness I post the bad image: