Why should the problem come from the p2pool ?
I run the http://p2poolcoin.com:6356 and after comparing the code, it's exactly the same code as a darkcoin pool (X11 too).
The only thing that is weird, it's last time i have check, the network was far away from 69Gh/s, this is very big !!!

Maybe a auto switch pool special X11 has raped this coin ? (does a such pool exist ?)