Slider height automatic resize leaves blank area under images

To see what I mean: Go to the Parabola demo site at http://demos.cryoutcreations.eu/wordpress/parabola/

Slowly start resizing the browser window width, starting from fullscreen – the moment its width goes below the slider width, a white space appears below the image, but clearly within the slider area. If you keep making the window smaller, at some point this white space disappears and the (resized) image fills the entire slider area again.

This happens even if no captions are set.

I would like the image to always fill the slider area – without any space below it.

I have uploaded a picture where you can see two differently sized parabola demo sites next to each other. Left side has the issue, right side is what I’d like it to look like all the time.

http://postimg.org/image/q07enazf1/

I assume it’s nivo slider that is causing the problem – none of the other Cryout themes has this issue.