I found a bug in the ValueTrees part of the demo. If you try to drag a node down within the same parent it gets put one position lower than it should. For example if you drag "You can drag around the nodes to rearrange them" between "...and press 'delete' to delete them" and "Then, you can use the undo/redo buttons to undo these changes" it will render after the last node not between.
This seems to fix it. Add these lines at line # 69. Basically if the new parent is the same as the old parent and the new index is greater than the old index you need to decrement the new index by 1.
if ((v.getParent() == newParent) && (v.getParent().indexOf(v) < insertIndex))