I've had many same-day SYD-MEL-SYD flights and it recognizes that as not a connection, but clearly an 18-hour connection is considered normal in PER (probably is ). More to the point the software is driven by the transit/stopover designation of the flight sectors as ticketed (which in turn affects certain fees, with stopover costing more than transit most of the time). Your ADL-PER-MEL-ADL was issued as all transits, apparently (saving you some money); would have been interesting to get an ADL-ADL baggage tag if you had chosen all 3 sectors (probably never see your bag again). That is one of the downsides of using the Q-tags, do you really know where your bag is going?