this is an excerpt from the book
Because of the way grid works one can only have one grid per controller function, unless they are embedded as components via
LOAD. To make the default search grid work in more than one LOADed grid, please use a different
formname for each one.
So, 2 steps required:
1. in the page that shows the grids has to have 2 different LOAD(), each one pointing to a single grid
2. use SQLFORM.grid(........, formname='grid1') for one and SQLFORM.grid(........, formname='grid2') for the other