I get the impression Ubuntu doesn't like Openfire, I'm using 6.0.6 and about every 12 hours I get disconnected with xmpp.client.idle set to -1, I've read up on their forums and others are having the same problem as me but it has yet to be resolved, one person jumped ship to Fedora Core and they say it solved the problem. I'm now using Openfire 3.3.3, while I was using 3.3.2 I was having the same issue as yourself so I would suggest upgrading if you haven't.
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