Create a grid with three columns A, B C, where A and C are indexed for sorting.
A B C
1 A C1
0 C C2
1 A C3
0 D C4
Now sort indexed column A and B:
A B C
1 A C1
1 A C3
0 C C2
0 D C4
Sort again with the same sort direction:
A B C
1 A C3
1 A C1
0 C C2
0 D C4
Row 1 and 2 are different compared to the first sorting (C3 and C1).