Marius, I suspect it is because the depth of the object/s does not change irrespective of width of display (eg many use the simple seperator and define the appropriate depth behind which the image will display).

I have in the past used a workaround which results in a responsive parallax image or slideshow. I create a transparent image (or a single colour image and set that colour transparent) roughly the dimensions of the desktop width and the height required. I then place this as an image in a text object or an image in the image object with the object being full width of page. Set your parallax image or slide show behind this row. As the page gets narrower not just the width changes, but also the depth of the row.

I have attached a transparent image 1024x400px, give it a try :-)