Post Slider – Strange configuration at 678px breakpoint

Since the latest update on the theme, there is a strange configuration on 4-column post sliders.

Here’s an example larger than the buggy breakpoint:

Here’s the buggy breakpoint:

Here’s smaller than the buggy breakpoint:

I checked your demo site, and the same bug is showing up there. Look on this page for the Latest Portfolio Entries without Excerpt:
http://kriesi.at/themes/enfold/shortcodes/post-slider/

Here are screenshots of the same sequence:

I at least fixed the CSS to get rid of the gray space to the right of the top image (and all images in post sliders):

.avia-content-slider .slide-image, .avia-content-slider .slide-image img {
width: 100% !important;
}

This is my guess what needs to be fixed in the grid.css file:

grid.css:678 @media only sc…px) and (max-width: 989px)
.responsive .av_one_half.first.el_before_av_one_fourth, .responsive .av_one_fourth.first + .av_one_fourth + .av_one_half, .responsive .avia-content-slider-inner .av_one_fourth {
width: 48% !important;
margin-left: 4% !important;
}

Let me know what you find. Thanks!