@checkcheck_master @CGBenner
Sorry for responding late.
Technically, the value of the iProperty is the formula. Therefore if you edit the iProperty in Vault, it will erase the formula and put in the value you specified.
This is similar to editing the property in Inventor, you have to edit the formula or it will be replaced with the value entered.
If the formula must stay, the property mapping should go in one direction, from File ->Vault. That way a user cannot edit the property inside of the Vault Client.
The reason this looked like it worked for the BOM edit is that you are editing the BOM which contains the value retrieved by the formula in the BOM, not the iProperty.
For Copy Design, as long as you don't have a rule that changes the iProperty value, the formula is not removed.