I'm running 6.0.2 of JIRA and using the ScriptRunner built-in script to create a sub-task as a post-function. Recently, the post-function stopped working and I traced it back to a permissions change I had made: I had removed the Anyone group from the Create Issues permission.
I thought the user that was initating the workflow transition became the Reporter for the sub-task and would therefore be the user account with the permissions.
Is there something else I'm missing here? Why does the create sub-task post-function require anonymous ability to create the issue?