Layer Slider > YouTube > the preview image is invisible

Hello support :-)
Please go there: http://www.augmented-banking.com and wait for the second slide, you will see a youtube video without the preview image.
And if you wait for the second slide, there is also a video who has the preview image.
I do not understand why because the parameters are the same for thoses videos:
The first one:
<iframe align=”middle” width=”889″ height=”500″ src=”//www.youtube.com/embed/oQxU7hJHDWk?rel=0&autohide=1″ frameborder=”0″ allowfullscreen></iframe>

The seccond one:
<iframe align=”middle” width=”889″ height=”500″ src=”//www.youtube.com/embed/_Z5PtIv1dRI?rel=0&autohide=1″ frameborder=”0″ allowfullscreen></iframe>

What i see in the backoffice :

What the users see:
http://s25.postimg.org/vhd8cho1r/without_image.jpg

Thanks