Fixed new article creation on customer change.

app/assets/javascripts/app/controllers/ticket_customer.coffee

@@ -26,7 +26,9 @@ class App.TicketCustomer extends App.ControllerModal
       @close()
 
       # update ticket
-      @ticket.updateAttributes(
+      ticket = App.Ticket.find(@ticket_id)
+      ticket.article = undefined
+      ticket.updateAttributes(
         customer_id: @customer_id
       )
 

app/assets/javascripts/app/controllers/ticket_zoom/sidebar.coffee

@@ -80,7 +80,7 @@ class App.TicketZoomSidebar extends App.ObserverController
       )
     changeCustomer = (e, el) =>
       new App.TicketCustomer(
-        ticket:    ticket
+        ticket_id: ticket.id
         container: @el.closest('.content')
       )
     @sidebarItems = [