I've seen this issue too, and have not yet been able to figure out the cause. I didn't realize it was affecting all nodes on the network at the same time. Thanks for pointing that out, it's useful information.

If you're running one of the nodes that does not have this issue (siberia.mine.nu:9338 and p2p-spb.xyz:9338) could you please contact me and let me know which version of bitcoind and which version of p2pool you're using?