This issue is because Webkit browsers only fire onmousedown events on scrollbars, but they never fire onmouseup events on them, so they JQuery UI draggable behaviour can never know when the mouse has been released. This is a bug in Chrome that has been there for many years without getting fixed, as can be seen in this thread:
http://code.google.com/p/chromium/issues/detail?id=14204
The same bug has been reported several times to jQuery UI, but it has been closed as won't fix or as invalid, since it's not a jQuery problem per se, and there's nothing they can do about it:
http://bugs.jqueryui.com/ticket/6925
http://bugs.jquery.com/ticket/8184
http://bugs.jqueryui.com/ticket/7935
Likewise, we do not do any special handling in our code to cause this issue, neither jQuery UI does. So, this issue can't be fixed. The only thing that could be done is to simulate an onmouseup event on a subsequent onmousedown event that the user generates, which would fire only for Webkit browsers and only if the current state is 'dragging'. This has the only objective of avoiding getting stuck forever with the draggable item in some way, when clicking the scrollbars for dragging.
Support Case #11873