STACK is not enforced (and an identical selection is allowed)
With the Advanced Test Set - Create Lawful Good, Hughpert Case Won, 1st
level MonKee (Choose MonKee on pop up)
Switch to Feats and Abilities
Add 8 to your feat pool.
Go to the 'Chooser' tree and open it up...
Select Choose String Stack once, selecting a single item
Select Choose String Stack again, selecting the same item again (this should not even be an option)
Committed revision 24042.