There appears to be an issue with p2pool producing lots of orphaned shares if the blocksize is greater than about 750 kB. This is caused by the limit on the number of transactions per share being too low.
https://github.com/p2pool/p2pool/issues/274As Bitcoin Classic sets the default block size limit to the largest allowed by the consensus rules, this can result in Bitcoin Classic nodes failing to produce valid shares. Consequently, if you run Bitcoin Classic with p2pool, you should use blockmaxsize=750000 or lower in your ~/.bitcoin/bitcoin.conf.
Hmm... not much good using a fork designed to increase the max blocksize limit if you can't... increase the max blocksize.