I think the way http://eligius.st/wiki/index.php/Shared_Maximum_PPS phrases it is confusing, but the line "If not, the miners are paid proportional to available funds.", in addition to this equation in the pseudocode: Pay each miner PPSamount / idealPayTotal * availableFunds, tells us what happens on long rounds. There is no mention of a payout queue; but it doesn't simply revert to proportional payment of 50 BTC. Instead, if switches to proportional payment of the 50 BTC plus the entire "buffer" from short rounds, instantly depleting the buffer.