Symptoms

After changing the event on a rule and creating a new rule for the original event, you get the following error when you save the form...
Cannot insert duplicate key row in object 'Form.Event_Design' with unique index 'UX_Form_Event_Design_ID_ContextID'.
 

Diagnoses

It appears as if there is some XML that gets "left behind" on the form when making changes like this. When saving the form, there is already some entries in the DB and this causes a conflict and displays error.
 

Resolution

We worked "around" the by "moving" the events on the original controls to hidden buttons, then deleting the original controls and recreating them again. This was routed to LABS and they logged an item in TFS. LABS confirmed that there is not a "cleaner" way of working around the issue.