I know the findaway's thread highlights an additional tax that is levied on one ways but have we been able to figure out whether this is a "real" tax that some countries add for one ways or just another Southwest IT glitch that can't compute correctly?
Their crack IT actually saved me some money when it forgot to charge me for the Belize departure tax so at least it works both ways (although it appears that problem has since been fixed when I try a dummy booking).