Please check the parameters at server side – i.e echo all of the posted data and see what is wrong. If data is not updated there maybe is a problem with a getted ID.
There is a similar post about this problem, but for now I do not have clear vision about what is happen. So, to resolve the problem if possible please send me a link or post it here.
One possible solution is to use loadComplete again with UI sortable. Do not have time to realize this. One simple solution is to allow dragging only on tr of the grid. Will be happy to see a working solution