The Subnet tree on the left side of the Manage Subnet page is very unpredictable, and often frustrating.
Many times when you open a supernet, edit a supernet, or drop a subnet in a supernet, the cursor focus will skip to some random spot on the tree. Not every time, but many times.
I created a video of what it looks like when this happens: ipam-inteface - DanSmart's library
Note that there seems to be two lines that are highlighted. That seems to be another problem. You need to click the item twice to get the focus only on that one line. If you click edit without clicking twice it edits two items.
Also when the cursor focus jumps, it seems to jump to the other highlighted item. Not necessarily random.
Dragging subnets is very tedious, Since you have to hover right at the top border to get the screen to move: Not too high or too low, and you have to wiggle the mouse.