I created an account on your site, and did the same steps as what I did on my site, and it came up with the same results. http://www.reeftalk.com/gallery/show...r/2729/cat/500
I uploaded test1.jpg (test one image) to the reef gallery.
I uploaded test1.jpg (test two image) to the coral gallery.
I then edited test1.jpg (test two image) and moved it to the members gallery.
I then edited test1.jpg (test one image) and moved it to the members gallery.
It overwrote the photo. Now both show the test one image. If I were to delete one, it would show no thumbnail for the other.
So this issue is in your gallery as well.