Delete Goal in Performance Document is not going through approvals process

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We have approvals in place if an Employee deletes a goal from their goal plan, it goes to their line manager for approval.  I have found today that if the employee selects delete against the goal after it is pulled into a performance document, it deletes the goal from the goal plan without going for approval.  Is this correct?  I am thinking at present the only way I can stop this is to personalise off the option to delete the goal and leave 'Remove from document' option but I am keen to understand why it isnt going for approval?