Problem selecting multiple rows in windows datagrid with shift-click

I have a datagrid on a windows form in a vb.net application. When I run it either in debug mode or from a build on my developer machine (winXP) I have no problem.
But when my users run it (both on XP also) from the build installed on their boxes, they experience the following:
1. when datagrid first loads, select the first row.
2. scroll down to some point farther in the list, so that the first, selected row is no longer visible in the grid (but is still selected, of course).
3. holding the shoft key, click any row to attempt to select all rows from the beginning to the clicked row.
4. instead of the desired result, just the shift-clicked row is selected.
5. HOWEVER, if the user then clicks in a cell of the datagrid (any cell, it doesn't seem to matter), then repeats the step, the mutiple selection now works.
6. Note that if the first row is still visible, then there is no problem - only a problem when all painted rows are unselected.

Unfortunately, as I said, on my dev machine this never happens - shift-select always works as expected.


Thanks for helping...
Ian