When attempting to edit a transaction that has the status 'Reconciled' will usually trigger a warning 'Change Reconciled Split?' if that warning has not been disabled by the user.

I believe that this is the desired behavior when the edit is attempted from the register containing a reconciled split line.  

This also works for the num, description and notes fields of the transaction while editing in the reconciled account register.

However, if the edit of those fields is attempted from the register of a split line that is not reconciled, the warning is not triggered.  This allows the appearance of those fields in the reconciled register to be changed arbitrarily from another register.  

Those fields should have the same protection in every register.  It may be preferable to create a new warning to apply when editing common fields in split transactions.