Hi,
I'm not quite sure why 'posting date' is listed in your source fields. What logic do you base on this field?
Anyway, as you saw by yourself, you cannot expect the system trigger this rule during master data creation. Further, during acquisition, derivation would work for logistic/financial document and not for already posted master data. You should exclude 'posting date' from the rule, which is responsible for master data.
Regards,
Eli