Queued Jabber notifications don't get delivered

Queued Jabber messages don't get delivered here, but if I disable message queueing, they get delivered.

Steps to reproduce:

1. write a PM to a user with Jabber notification turned on (posting on a watched topic probably would work too)
2. there is a cache/queue.php with content which looks sensible
3. wait some time until the queue run is called
4. the queue.php seems to be gone but no Jabber message is sent

Messaging via the Jabber profile link works - probably because it is not queued.

Using:

php 5.1.4
Tried jabber servers: jabber.ccc.de and a own one running jabberd 2.0.11