I had a look at Image.transform, and it looks like new_wand is being used as the source and the destination. In the code below, I've placed the result of the transformed image into a new resized_wand image and it appears to work, although I am unsure whether new_wand gets destroyed correctly.
Thanks for reporting this, and sorry for the 5 year delay. You are correct with new_wand being reused, and introducing issues with animations + memory leaks. Holding off on paging reset as folks disagree with default behavior, and transform is also being deprecated. In fact, it was removed in ImageMagick-7.