Yes, you are correct the demo does the same thing on both the ipad and iPhone. I figure it had to be in the java script. When you do the responsive setting it does not do that but I could not zoom at all.
When you click on the image and it open up where the background is darken, I believe that is the lightbox screen. The images is in the center and the problem start when you do the pinch to zoom in. It then shoot down, when you try to scroll to find it the image keeps moving down. You can never select it and the only way you can is if you pinch to zoom out. To me it looks like the screen is forcing it to stay center, because the website page zoom also when you pinch and zoom. I have this problem with the velvet theme also, I figure I can’t be the only one having this problem, but like I said my client does not like the responsive setting and the reason why I am going through this.