Hi,
I had no such problems editing the tab order, make sure you switch it to custom and drag it to a new location.

If you are still having trouble, you could bypass it with an exit event for the cell.
form1.#subform[0].Table1.Row1.TextField1:exit - (JavaScript, client)
xfa.host.setFocus("Row2.TextField1");
then in Row2.TextField1, have some code that when exited it will focus on Row3.TextField1 etc.
The catch is though, it will always fire on exiting the field whether you press tab or not. If you exit by clicking the mouse somewhere, the focus will go back to the next field in the code. If you clicked in another cell in the table, it will focus on the cell in the code.
If the form will always go from one to the next, then there is no issue.