jQuery UI Sortable serialize not working!

Question

The notes on UI Sortable 'serialize' says it creates a passable array based on the ID of the sortable list. You're supposed to use an ID with a name and underscore "foo_" and it creates an array -> foo[1], foo[2], etc. However, it does not work. I'm getting a result that looks like this: '[] = foo_1, [] = foo_2, etc. Has anyone else had this problem and know what the fix is?

    var linePositions = mlo.sortable('serialize');