Flexslider not showing first image downloaded from wordpress site

I have a flex slider that loads images from a wordpress site via xmlrpc and plays. Looking through the elements, I saw that all images are loaded correctly, but only the first image is not displayed. I found out that the ul will have translate3d (-1320px, 0px, 0px) if I'm in the first image.

Here's an example of the result:

<ul id="div_slides" class="slides" style="width: 3200%; -webkit-transition-duration: 0s; transition-duration: 0s; -webkit-transform: translate3d(-1320px, 0px, 0px);">
<li class="clone" style="width: 1320px; float: left; display: block;">
    <img src="http://www.cugatcasas.com/wp-content/uploads/2015/06/IMG_7805-300x200.jpg">
</li>
<li class="" style="width: 1320px; float: left; display: block;">
<img src=""></li>
<li style="width: 1320px; float: left; display: block;" class="flex-active-slide">
<img src="http://www.cugatcasas.com/wp-content/uploads/2015/06/IMG_0638-300x225.jpg">
</li>
<li style="width: 1320px; float: left; display: block;">
    <img src="http://www.cugatcasas.com/wp-content/uploads/2015/06/IMG_0639-300x225.jpg"></li>

      

        
        
        
      

    

image IMG_7805-300x200.jpg (first) is not displayed. Is it because of Wordpress answer or because of slider (translate3d)? How to avoid this?