drag item outside the div of treeOption cause lost of data

[Sczlog]

ATTENTION: I find the data didnt lost but inside the last node and be its first child,that problem only show up when all the child node is collasped and you drag the other first level node and drop it to the last one.

I try to make a dragable configure menu with ui-tree, but when i try dragging the first item to the end of last item, the first item should be showing in the end but it disappeared. Seeing it like when drag sth outside the div , it disappears. I has done the same thing on the demo page and it happenned every view but not in the connected tree one. I'm using the latest ui-tree and 1.6.x angular.