I'm not sure where I heard it or read it, but the way I know is that you want a single owner for every issue (user story, bug or task). There may be different subtasks of that user story that may be assigned to other people, but ultimately the owner of the user story reflects the person that is ultimately responsible to make sure that user story gets done. That person should be the developer that will do the work. The developers usually prepare a testing subtask for the user story when they are tasking it for themselves. The testing subtask may be re-assigned to other testers if needed and testers may create additional testing subtasks based on what they see. If they find bugs, they can create subtasks under that user story to fix it before the sprint end. If it looks like the bug will not be fixed before the sprint finishes, it can be turned into its own bug (issue, not subtask). But ultimately, the developer is responsible to make sure it goes through all phases.