If you mean the last-name sort on the authors tab, then that is broken in the current 4.7 and I think 4.6 firmware versions, it sorts names beginning with a lower-case letters at the end after upper-case Z. I don't think there is any way to solve it.
Edit: See the second screenshot in
this post for an example of the problem I am describing: it sorts le_Carré at the end because the first letter of 'le' is lower case. (It sorts Le_Guin correctly.)
Edit2: Also, the name has to be entered in "First Last" format, "Last, First" no longer works in recent firmware because the comma is now used to separate multiple authors.