How do I stop goal updates from syncing real time to a Performance document after it's already start

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Hi All!

We have already begun our 2018 Performance cycle for the year.  We ran our eligibility and employees are starting their Self Evaluation. 

We are finding that if an employee has started their Performance evaluation and then goes back to one of their goals in Goal Management and makes a change/update, it is then syncing this change/update back to their Performance goals in the Performance document .  We do not want this functionality.  In years past, once the employee started their performance evaluation, the goals were "locked down" and reflected a point in time view.  

Any ideas how we get these "locked down" again, so there isn't a real time sync between the two?