For the love of god, please remove the integration of the old bastard, jquery ui!
For example. The structure field dragging is horrible, on mac os x (safari, firefox, chrome),
its jumpy, slow etc…
Try this instead : https://github.com/RubaXa/Sortable
Demo : http://rubaxa.github.io/Sortable/ ( no jquery : )
So freakin smooooth operator…
It’s been the taking point of this topic: Kirby Size Inventory
Trying to find ways to optimize the Kirby Panel without sacrificing features.
I admit Sortable does look pretty smooth.
Thanks for the feedback. I’m marking this as solved though as Bastian is already aware of this as @PaulMorel wrote.
For some Cordova apps I use http://johnny.github.io/jquery-sortable/
It’s pretty slick and small in size, even IE7 is supported (not that this matter for apps, because I use the Blink render engine for IE11 and Edge).
Depending on your needs, this extension can come in handy (it creates OL and UL lists for all the items, so it maintains the html-structure / semantics).
Another cool features is the menu-sortable-option;
http://johnny.github.io/jquery-sortable/#bootstrap
This way, you can build / create drag 'n drop menu’s, like Wordpress does 
Nice, extended demo with display logic;
So I hacked the form.min.js
https://github.com/A-Monkey/smoothDrag
Just replace the form.min.js in panel/assets/js/dist/
Fire up a structure field and you are good to go… ; )
Ps. I added a style tag in structure/template.php
Remember this is just a hack… don´t use it in production, but hey it works i thiiiink… ; )
<style>
.sortable-chosen { opacity: 1; }
.sortable-ghost { opacity: 0; }
</style>