Problem with WP Lightbox 2

Hi,

when the wp lightbox 2 plugin displays a picture on screen, the responsive drop down version of the navigation menu shows up righ underneath the original menu bar.

Have a look at https://www.prilisauer.at/fotogalerie/ and click on the picture in the post below. after closing you’ll see the additional drop down menu.

How can i get rid of this? I’m using the wp lightbox 2 plugin with other responsive design themes and the problem just occurs with “clean retina”

regards