Then I'd have to say there was a lingering bug of some sort because somewhere in the 20 minutes it must have gotten the work info from bitcoind since bitcoind is saying it's generating GBT with the CreateNewBlock message. Check if you have the p2pool logs prior to that block find for some kind of unhappiness there.
Indeed. There is something wrong here, but I don't have much feedback other than empty block and logs that show processing work. Then the logs look normal except for
2016-04-14 23:21:13.403123 > Block submittal result: False (u'duplicate') Expected: True
It may be some sort of bug.