No failure message while trying to register user with existing email address

[ahoquegh]

Hi
At the sign-up window while I tried to register a new user with an already registered email address ( different user name) the registration failed. But no message poped up to alert the prospective user that the registration failed. ( however in the app log does show an ERROR: duplicate key value violates unique constraint "users_email_unique")

Is there a setting to enable the failure message notification during registration? or is it a bug?
Appreciate your replay and suggestions. Thanks in advance.