sorting datagrid with empty rows

Question

I have datagrid that I'm filling with rows, if the rows don't fill up the size of the grid, then I'm adding new empty rows from my dataview in my derived datagrid. The problems that comes up is that when im sorting the columns the empty rows are also sorted (not the last one, and i don't know why the last one is not sorted). Qestion: can i somehow sort the filled rows and just letting the empty (DBNULL) just be in the bottom of my grid?