I'm inclined to believe the memory leak... although I've only seen it on my Linux (Ubuntu 14.04) node. I watched bitcoind spool up to consume 8GB of RAM before it was shut down. On my Mac, using the same codebase, I regularly only see about 400MB of RAM being consumed by the bitcoind. Both Linux and Mac are built from source.
Are both bitcoind nodes being used for p2pool? My testing indicates that the use of getblocktemplate is necessary for the memory leaking to occur.