Back to load balancing again... Incredible how 10 mins into load balancing and expected Slush payout has halved despite 24 hours of full speed contributions! Hmmm...
You know, this is something... I have noticed the inverse as well - I plugged in a new miner 11 hours in, effectively doubling my hashrate, and an hour later the pool found a block and I got a payment proportional to if the new miner had been mining the whole 12 hours.
It seemed my share of the payout was calculated on the past hour - not the whole 12 hours I had been mining at 50%.