I take the point, but it's hard to know whether anything is broken. Maybe it's working as designed, and that hidden bucket space on YVR-YYC is supposed to be available only for folks booking that single segment, not that segment as part of a longer trip. There could be lots of reasons for that, including that YVR-YYC is (I'd guess) much more expensive as a short trip than as part of a longer itinerary. My local example is YOW-YUL (or YOW-YYZ). It adds almost nothing to the cost of a TATL departing YUL. But if I just tried to fly YOW-YUL it could easy be $500 each way. It wouldn't be surprising if AC gave some hidden bucket space to folks flying YOW-YUL as origin/destination that they don't offer to me flying YOW-YUL-FRA and getting the YOW-YUL segment more or less free.

(YYZ would have worked better on this example because so few YOW-YUL flights have anything other than Y, but you see the idea.)

Edit: I should have said the fact it advertised upgrade space on all four segment shows something is broken, but it's unclear what.