The way I understand SMPPS from reading here:
http://eligius.st/wiki/index.php/Shared_Maximum_PPSand from talking with luke-jr and reading some of his other posts...
SMPPS does not "carry debt". If/when the scenario rises that the total payout exceeds the block income plus the reserve funds, then the pool simply divides the block income plus the reserve by however many shares there were that round. This leads to a situation where the SMPPS shares are worth less than their advertised price. But, that is all. When the next round starts the the pool has 0 reserves and 0 debt.
The key part to this is the last part of luke-jr's pseudo code:
else:
Pay each miner PPSamount / idealPayTotal * availableFunds
Nowhere in there does it mention "remembering" the difference between the ideal payout and the realized payout. It simply switch to "proportional"
over the total available funds. So, technically speaking, unless the reserve fund is 0 when the payout exceeds the income, it never does true proportional.