Can you give me some more info? Why is that a correct image?

I have a dreambox 800 with the latest ****** image. The box is connected to a loewe connect 32 full hd lcd with the supplied dvi-hdmi cable. The problem is that sometimes when I changes the channel I briefly see horizontal lines. It doesn't happen all the time. I also see it when I exit a menu of the dreambox or when the screen fades. When I connect the box with the scart cable to the tv, these lines never appear. Does anyone have an idea what the problem could be? I have made a screenshot of the screen.

[Blockierte Grafik: http://www.imagebucket.net/bucket/is.php?i=3691&img=DSC_1468.jpg]