In the document on course copy/import (How do I copy content from another Canvas course using the Course Import tool? ) it says "You only have access to copy content from courses from current or previous courses in which you are an enrolled user." It doesn't mention the role the user might have had in the "from" or source course. With permissions we can control who can copy content into a course, but apparently not what courses they can copy from.
On testing, I find that someone with a TA role in a course is allowed to copy the content from that course into their own course (as long as they have privileges to Import Content). On the other hand, someone who had a student role is not allowed to do such a copy. Limiting students makes sense. But it seems to me that a TA role should also not be allowed to copy content into a course where they are a teacher.
Is this behavior intended? Is there any course permission we could use to limit which roles gives a user the right to choose that course to copy from?