Not sure if this is an issue, or a feature, but I'll report it anyways. I just tried adding two pictures to the beginning of pool #714, and discovered that hitting the order link from the pool page does two things:
-it loads every single image in the pool, which for large pools takes a long time (>5 mins in the aforementioned pool's case)
-it only loads up to the ~1000th image, which for pools > ~1000, makes it impossible to order pictures after a certain point
I found a workaround, by using the edit link from the pool menu, which lists all of the posts in the pool by post# instead of by image. It also lists all of the posts, no matter how large the pool is.
As I said, I'm not sure if this is the way it's supposed to be or not, but maybe, when a pool grows beyond a certain size, a different interface could be used instead, e.g. something similar to the edit interface, or maybe just direct the user to the edit interface, or possibly a notice to the user on the order interface about using the edit interface for large pool sizes.
This is because even if all of the images in the pool had been displayed in the example I mentioned, it would have been extremely ungainly trying to drag and drop an image from the end of the pool all of the way to the beginning, or to anywhere in the middle if that was the case.