One can book an "open leg" ticket with many airlines for half of the sum of the two return fares... An open leg is a flying from place A on one continent to B on another, and then flying from C on the same continent as B back to A. Or a ticket from A to B (on another continent) and back to D (on A's continent.) Certainly worth to investigate if you're planning to do some ground travel.
Another issue with online reservation systems is that a fare will be held for someone from the moment a website makes a formal offer till the payment is done... Some people bail out of that process and that could mean that some low-priced seats reenter the pool. If they were the last available for that fare it will mean that visible quotes showed higher fares in the mean time. (It's also possible that a "yield manager" sees weak sales and throws a dozen of bargain seats in the market.)
Yes, Airline pricing is incomprehensible.... confusing the competition seems important!
