Is the individual author sort value correct for Hamsun? In the tag browser on the left-hand side, right-click on Hamsun and choose 'manage authors'. Verify that the sort value is what you expect.
Edit: Take a look at
https://www.mobileread.com/forums/showthread.php?t=98470, which is a long discussion of author sorting on the kindle. There might be something there that helps explain what is happening