Empty view.
Split in 2 or 4.
Add 10 lines.
Scroll to top in all panes.
In other pane(s), the current line is 10.
In the active pane, the current line is 5.
Press Enter once.
** I see the line number area in other pane(s) is:
1
2
3
5
6
…
Undo.
** I see the line number area in other pane(s) is:
1
2
3
5
5
…