[redmine]allow you modify your parent later without changing the tracker id

backlogs_issue_patch.rb

# plugins/redmine_backlogs/lib/backlogs_issue_patch.rb 
def backlogs_after_save
     # ..
     # omitted 
     # ..
     if self.story? 
         # omitted 
         
         tasklist = RbTask.find(:all, :conditions => ["root_id=? and lft>? and rgt<? and
                                          (
                                            (? is NULL and not fixed_version_id is NULL)
                                            or
                                            (not ? is NULL and fixed_version_id is NULL)
                                            or
                                            (not ? is NULL and not fixed_version_id is NULL and ?<>fixed_version_id)
                                          ) and tracker_id = ?", self.root_id, self.lft, self.rgt,
                                              self.fixed_version_id, self.fixed_version_id,
                                              self.fixed_version_id, self.fixed_version_id,
                                              RbTask.tracker]).to_a
         # omitted 
     end
     # omitted
end