I may remove the parent-pooling feature. It was intended to allow things like "edited" versions of pools (crops, etc.) to make it easy to download the original versions, but it's too goofy. There's a lot of overlap between books where this doesn't make sense, with different versions of the same image in different books which should be parented but not affect pools.

It's fairly rare that this is actually needed (and it's not the easiest feature to understand, either); I think it'd be better to just create a second pool the rare times it's actually wanted.