Sortable: incorrectly considers hidden elements as the clone element

Was recently working on a project when i came across some weird behaviour with draggables connected to sortables.

A simple demo is included. 5px border is to make the bug more visible.

What to look for:

1. The draggable is losing its size, watch for the floating border.

2. Dragging to the first column causes a second placeholder with size zero to appear in 'random' placec in the same sortable.

Fix:

Disabling the hidden sortables. In the demo:

$(".sortable:hidden").sortable('disable');

Comments:

Static sizing the elements fixes problem 2, but not 1.