When logging new workitems, Planner "remembers" labels from most recent workitem

[ldimaggi]

Steps to recreate issue:

• Create a new workitem using the detail view - assign one or more labels to the workitem
  

• Save that workitem, return to the backlog view

• Create another new workitem - observe that the labels from the previously created workitem are pre-selected:
  

• Observe that the labels' pre-selection is not indicated in the lable drop-down list:
  

The user must manually unselect the labels.