There was no house wrap beneath the corner boards. Over time, the corner boards and the wood siding will shrink and expand. Certainly the intersection between the corner board and siding will not be water tight. Yet there was no protection provided at this point. This example demonstrates the overconfidence builders have with well-installed siding.
Many builders fail to place house wrap beneath corner details.
An often-heard strategy involves caulking the joint between the siding and corner board. In my opinion, caulking only makes matters worse. It retards the drying process when water penetrates the corner detail. I think that building a forgiving corner joint is the best design. Sealants should not be used as a primary membrane material in wood-frame construction.