Those calcs are created in the data source before you read the data source into Tableau. I'm guessing the data source is a published extract.
At our shop we have decided never to create calcs in the original data source specifically for this reason.
Yeah- it is using a published extract. Good to know, will help me avoid the issue in the future.
So whatever workbook you use to publish it from, you can edit the calc there and republish.