Incompatible with ejabberd dialback implementation

I noticed an incompatibility between ejabberd (2.1.0) and jabberd2 (2.2.8 .. sorry, but the server is not in my control and they decided to use the Debian version) when the server connects the first time (but the second try works). Here an example:

connection 0
ejabberd -- connection start -> jabberd2
ejabberd <- connection start -- jabberd2
ejabberd -- send dialback key -> jabberd2

connection 1
ejabberd <- connection start for verify-request -- jabberd2
ejabberd -- connection start -> jabberd2
ejabberd <- send dialback key -- jabberd2

connection 2
ejabberd -- connection start for verify-request -> jabberd2
ejabberd <- connection start -- jabberd2
ejabberd -- send verification -> jabberd2
ejabberd <- verification ok -- jabberd2

connection 1
ejabberd -- report dialback result -> jabberd2
ejabberd <- send verification -- jabberd2
ejabberd -- verification ok -> jabberd2

connection 2
ejabberd <- report dialback result -- jabberd2
(shouldn't this go out through connection 0?)

ejabberd will close connection 0 after a while:
ait_for_validation: ejabberd -> jabberd2 (connect timeout)

ejabberd will create a new connection (but this time it is successful)

connection 3
ejabberd -- connection start -> jabberd2
ejabberd <- connection start -- jabberd2
ejabberd -- send dialback key -> jabberd2

connection 1
ejabberd <- send verification -- jabberd2
ejabberd -- verification ok -> jabberd2

connection 3
ejabberd <- report dialback result -- jabberd2

.... beautiful stanza stream....

Now my question: Why is jabberd2 sending on connection 2 and not on connection 0 (this is where the verification was started)? Isn't this a bug in jabberd2?