Due to reasons unknown to me (but undoubtedly involving politics and gerrymandering), when the light rail was extended to Hillsboro several years ago, everything west of the zoo was put into zone 3. There are no zone 2 stops between the last stop on the west side (Sunset transit center) and the zoo stop halfway through the west-side tunnel (which is in zone 1).
What this means is that anybody buying a ticket out in Hillsboro is going to need either a one-zone ticket or a three-zone ticket. There are no possible destinations from Hillsboro that would require a two-zone ticket.
However, the ticket machines at these stops only sell two- and three-zone tickets! I hope there's some other explanation, but it certainly seems like Tri-met is ripping people off. The amount is small (the one-zone ticket is only five cents cheaper), but the principle of over-charging is the same nonetheless.
I need to purchase a three-zone ticket anyway so this doesn't affect me directly. But I am curious as to why such a blatant error/oversight persists.