order of vertices in input file

One simple question:
Why are the results different when I just change order of vertices on one line in input file? The graph is same, so I would expect that results will be same too. But this change affect result of my program. When I order vertices on the line, I get usually much better result (but the speed of generating input file is much slower). The program used is gpmetis.exe.

Example of unordered graph (only part shown):
395584 530071
2 3 4
5 1 6
1 7 6
8 9 1
10 11 2
2 12 3
13 14 3
10 4 15
15 4 16
5 8 17 18
5 19 20
14 6 21
7 22 23

Example of ordered graph (only part shown):
395584 530071
2 3 4
1 5 6
1 6 7
1 8 9
2 10 11
2 3 12
3 13 14
4 10 15
4 15 16
5 8 17 18
5 19 20
6 14 21
7 22 23