prevent drop in userstory in taskboard

app/coffee/modules/taskboard/sortable.coffee

@@ -62,6 +62,7 @@ TaskboardSortableDirective = ($repo, $rs, $rootscope) ->
                 copySortSource: false,
                 copy: false,
                 mirrorContainer: $el[0],
+                accepts: (el, target) -> return !$(target).hasClass('taskboard-userstory-box')
                 moves: (item) -> return $(item).hasClass('taskboard-task')
             })