I don't know if anyone else has seen this problem yet.
1. Create three pages
a. Page 2 and Page 3 are children of Page 1.
2. Create a menu and add pages 1,2 and 3
Place pages 2 and 3 under page 1 as children of page 1.
Save the menu.
The menu label for Page 2 will change to the menu label used by page 1. The menu label for page 3 remains as page 3.
Can anyone else reproduce this problem in their installation? Changing the menu label for page 2 always reverts to the menu label for page 1 after saving the menu. If you remove page 2 then the label for page 3 is changed to the label used by page 1.