I had this as well. The home airport was London Gatwick, and the other entries were Bangkok, Khon Kaen, and Singapore.

It seemed to me that it couldn't find a route from London to Khon Kaen (Khon Kaen isn't an international airport), but interpreted that as a zero cost flight. The route it gave me was Gatwick -> Khon Kaen -> Bangkok -> Singapore and the cost for the whole thing was a fraction of what it should have been.

The way to make that route work, by the way, is to go Gatwick -> Bangkok -> Khon Kaen -> Bangkok -> Singapore (or throw Chiang Mai or Hat Yai into the mix). You can only reach Khon Kaen by air through internal flights in Thailand.

just another, not sure if it will help. san jose international - home start, date 2017/05/02

berlin,3 days

boston, 3 days

shanghai, 3 days

http://imgur.com/dcLXmlr

I've booked marked it. Cool site.