Draggable only works once

[MBing]

In this plunkr when you try to drag the items on the right. You can see it is working fine,
but when you try again, it doesn't change anymore.
http://plnkr.co/edit/6s03Gq

So basically when you drag 'subitem 0_0' below 'subitem 0_1' it will work fine,
But then when you try to drag it up again to its original position, 'subitem 0_1' will stay on top.
(It's the same when you first drag 'subitem 0_1' up and try to drag it down again.)

N.B.There is another issue in this plunkr, but I will address that in another issue. #59

[MBing]

Same solution as in #59
I changed ng-repeat="subItem in currentMainItem.subItems track by $index" to
ng-repeat="subItem in currentMainItem.subItems"

and it all worked fluently!
So closing this and plunker is updated.