Ranking setting is copied to all tasks from one task

I have an issue with 'Ranking in Custom Project'. When You create such a project, add tasks, set ranking: 

   Task -> Full Settings -> Ranking

and run it. Then ranking is different in every task as set originally.

Then after running it one or a few times, change ranking in one of the tasks.

It starts changing then rankings in all of the tasks in the whoe Custom Project tasks to the same configuration.

Please find attached screen.