disable a sortable while dragging with connectedLists

disable a sortable while dragging with connectedLists

Hello,

it seems to me that it is impossible to disable a sortable while dragging an element from another sortable.

Here is little more information:
I have multiple (more than 3) connected sortables. Think of it as lists of assigned tickets and another list with unassigned tickets. However the another list may also display all kinds of tickets, so it is possible that one entry is present in two (and at most in two) lists. So I want to prevent dragging an element from one list to another list that contains the same element.

I could've think of two approaches:
a) while dragging check all other lists and do the magic
b) after dropping check the target and revert if item is already there

Here is how lists are inited:
  1.       $('ul.has-tickets').sortable({
  2.         connectWith: 'ul.connected-sortable',
  3.         handle: 'span.cmd-drag-drop',
  4.         receive: list_receive,
  5.         start:list_start,
  6.         stop: list_stop,
  7.         update: list_update
  8.       });
And here is the start callback:
  1.   var list_start = function(event, ui) {
  2.     var twin_id = _get_twin_id(ui.item[0]);
  3.     var $target = $('ul:has(li[id='+ twin_id +'])');
  4.    if ($target.length > 0) {
  5.      $('#'+ $target.attr('id')).sortable('disable');
  6.   }
  7. };

I'm however hitting problems.

Appraoch A:
Prevent dropping. Two possibilities: either disable the sortable or place an element above it. Neither is working. $('#target').sortable('disable') is called in the start callback handler and has no effect while dragging an item; the sortable is disabled after dropping. Placing an element over the target is no problem, but the list still accepts items.

Approach B:
I can't seem to be able to find a reasonable way of returning the item back to the sender to the same position. I have the sender in ui.sender but not the index number.

Any hints are highly appreciated.

Thank you for your time.