Error from gateway during jabber:iq:gateway protocol results in bogus JID being added to roster

When I enter an invalid legacy username into the Gajim "add a contact" dialog set to talk to a gateway, the gateway returns:

    \<iq id='267' type='error' to='[redacted]' from='[redacted]'>
    \<error type='modify'>
    \<not-acceptable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
    \<text xmlns='urn:ietf:params:xml:ns:xmpp-stanzas' xml:lang='en'>Only US/Canada telephone numbers accepted\</text>
    \</error>
    \</iq>

but instead of displaying this or any other error to me, Gajim treats this as a signal to just use the raw string I entered + "@component.tld" as the JID. This results in a bogus JID in my roster.