very interesting observation.
edit: just checked Block #180966 via http://www.blockchain.info/block-index/229374/00000000000009109a556cf6c997f1ec10afa32fa53064b59a5fa0c026d200ee
and it really says relayed by p2pool while the distribution of mined coins looks unusual
but the blocks you mention are quite old (may 22 - may 28). did you see one recently?
meaning if it is common or just happened few times
Looks like these blocks was mined by solo players (input not split to miners).
All of them are directed to:
18tyJrqKKcHdJ46th2icwoKZBZVp6qUsTx 47.90167571 BTC
1MgH8iNkdZrDW8rsfzifDzsqJnCjBVyRBV 2.50787429 BTC
1MgH8... is mining at p2pool @10GH maybe he also mine solo...
not sure if solo mining with 10GH would net 6 blocks in 6 days.
also not sure if first relay info recorded at blockchain.info is 100% correct
if it is a solo miner I would bet he's running much more hashing power and directs only 10 gh/s of it to p2pool for whatever reason
i can also speculate that it is computable and possible to patch default p2pool miner to behave like this. either a bug or tuning
address in OP mined so far 250 btc in transactions corresponding to p2pool mining payout
address 18tyjr looks like 9 block reward.