Solved the problem!
in the nggallery.css stylesheet, changed this:
.ngg-galleryoverview {
overflow: hidden;
margin-top: 10px;
width: 100%;
clear:both;
display:block !important;
}
to this:
.ngg-galleryoverview {
overflow: visible;
margin-top: 10px;
width: 100%;
clear:both;
display:block !important;
}