3820669 - Why for some airlines Business Class is available in the dropdown but only Economy fare was offered in Search by Schedule?

I was trying to search flights in Business Class, however, due to the cabin not being available, it was showing in the "mixed results" with Business for the long haul and Economy for the short one. But then, when asking to price it, it flips the whole flight back to Economy.

When searching for Business class for International, in one leg, if Economy is available, and the second leg has Business in Shop by Schedule, the Cabin class changes to Economy after pricing. , KBA , CON-CA , Cross Applications , Problem