I was checking to see if the fare had changed for an upcoming trip and while cycling through the options found that premium could be a pittance more than value and much less than flexible.
We've reserved a roomette but if this occurs elsewhere it could be a loophole for somebody.
That was starting in SNC and appears to be the usual BC surcharge. I was able to do the same thing combining BC on the Cascades with coach on the Builder. It appears that the rule is: if any segment is in an upgraded class, the price drops to value + upgrade but retains the 100% refundability of flexible. Not terribly useful but still not what I would expect.