Yup...that fixed it. Darn, I should have caught that one. 
However, your absolutely correct fix ONLY works IF the delete happens AFTER the save.
If you comment out the delete section after the save, and remove the comments on the delete section before the save (and replace launcher_id with key as you so astutely pointed out), the code still breaks in that the Preferences db is messed up (in the same way) as before.