Using java.text.Collator for ordering by lastnames makes a bad sorting order because Collator doesn't count the blank spaces, as reported in https://jira.sakaiproject.org/browse/KNL-873
Given two students, whose lastnames are "Martinez Torcal" and "Martin Troncoso", the logical alphabetical order is first "Martin Troncoso" and after "Martinez Torcal", just because the blank space is counted as a character.
However, in our Sakai 2.7.1 they are ordered just the opposite: first "Martinez Torcal" and after "Martin Troncoso". This issue happens in every tool of Sakai which uses Collator. And Gradebook is included.
I have made a patch for 2.7.1 using RuleBasedCollator class which fixes the problem, but I'm not sure if could affect the performance.