I am using Enfold and suspect that Enfold is opening a gallery, as well as whatever GD does.

I am still on local host, but you can see a similar effect on this site, not using Enfold.

http://torontomindbody.org/events/workshops/yin-yoga-and-reiki-by-candlelight-with-cheryl-mckenzie/#post_images

Is there an easy way to disable the GD popup?

Thanks for spotting this.
To fix this issue, plz get attached zip, extract it and upload custom_functions.php in geodirectory > geodirectory-functions folder using ftp and then put this code in enfold child theme functions.php

add_filter('geodir_post_gallery_id' , 'geodir_post_gallery_id');
function geodir_post_gallery_id($id)
{
	$id = 'geodir-post-gallery-enfold' ;
	return $id ;
}

after this, plz put this css part in
wp-admin > geodirectory > designs > scripts > Custom style css code

#geodir-post-gallery-enfold a{
box-sizing: border-box;
	display: inline-block;
    position: relative;
    width: 24%;	
}
#geodir-post-gallery-enfold a:after{
	  content: '';
    display: block;
    margin-top: 65%;
}

#geodir-post-gallery-enfold a .geodir_thumbnail{
padding: 0px;
float: left;
width: 100px;
background-position: 50% 50%;
background-repeat: no-repeat;
background-size: cover;
min-width: 92%;
position: absolute;
top: 0;
bottom: 0;
left: 0;
right: 0;
margin:4%;
}

Plz let me know, this will be included in next release.

Thanks