Steps to reproduce the issue

Create a content field
Use the batch function to COPY the field
Publish the new field
Open an article for editing

Expected result

Field tab has TWO fields with the same label

Actual result

Field tab has ONE field only

Additional comments

When you create a field it checks that the generated name is unique and if not prevents saving.

When you batch copy a field there is no check and you end up with invalid data as you have multiple fields with the same name (but diffeerent id)