stories should have a well-defined order on all DBs

NULL should be in front (COALESCE)
and if the issues have the same id, the older one should win

lib/backlogs/patches/version_patch.rb

@@ -24,7 +24,7 @@ module Backlogs::Patches::VersionPatch
         # and add issues, that have a position, at the end
         stories_wo_position = self.fixed_issues.find(:all, :conditions => {:project_id => project, :tracker_id => Story.trackers, :position => nil}, :order => 'id')
 
-        stories_w_position = self.fixed_issues.find(:all, :conditions => ['project_id = ? AND tracker_id IN (?) AND position IS NOT NULL', project, Story.trackers], :order => 'position')
+        stories_w_position = self.fixed_issues.find(:all, :conditions => ['project_id = ? AND tracker_id IN (?) AND position IS NOT NULL', project, Story.trackers], :order => 'COALESCE(position, 0), id')
 
         (stories_w_position + stories_wo_position).each_with_index do |story, index|
           story.send(:update_attribute_silently, 'position', index + 1)