The mapping for the "generate documents..." function

Hi there

I tried this new funciton of "generate documents ...", which works fine. However, just realized one issue here.

I completed the mapping in one sheet, tested the mapping and got the PDF as we expected. Then I made a copy of this grid and tried to used it for a new project. When I open the new grid, seems the mapping is gone and I have to redone it again from scratch. Did I do anything wrong?