I have narrowed down the problem to somekind of bug or compatibility issue with using a checkbox in side of a data-grid on the same tab as listbox, specifically when the listbox contains the parent table and the data-grid contains the child table and SET RELATION is on.

In this specific situation, the check box in rows 2 forward can not be changed and the cursor automaticaly jumps back to the first record in the data-grid.

Any of the following issues causes the data-grid with the check box class to work correctly. 1) Turn off the set relation, 2) change the list-box for the parent table to a data-grid.