i banned a user by ban_set, and then went to my journal and deleted a comment they'd left. when i selected to also 'ban so and so' i got an error code attached to the end of the result text. the opportunity (or inclination) to reproduce the effect hasn't risen since.
Deleted The comment has been deleted. Additionally, user so and so has been banned from posting anything else in your journal.Duplicate entry '12402-68220' for key 2