I don't have skin in this game, but I find the thread sadly amusing, as joinery techniques are 100s or 1000s of years old. Someone took a shortcut or made a bonehead design move on the cabinets. Someone else said it best - these joints are cut on a shaper. Whether the shaper bit cuts this or a locking miter, like on the old Bally cabinets - same amount of time for the worker, once the tooling is set up. It looks as though the way the joint is cut, there's not enough wood left in that one spot, so that the wood and therefore joint is weak. Without enough wood or supplemental support, like blocking, to keep it rigid, the wood breaks.