This might not be something that you can help with the way touch support works.  But there are some issues with the way the iPad detects dragging the page vs the gallery.  If the gallery is embedded and takes up 100% width and height, sometimes it will detect an up and down drag as moving the page, and sometimes it will get stuck and just try to drag the image left and right.  It's just buggy, it can take a few tries to get an up and down page scroll to work.  Would there be any way to adjust the behavior to be less sensitive, to detect a page drag unless a large left or right swipe motion is made on a gallery image.  Or perhaps disable swiping on the gallery all together.