Thank you for your input...According to the US Forestry service:

"General:...It has a high density and decay resistance. It shows slight shrinkage and stays in place well. "

I wonder if your experience is common, or maybe related to the particular wood you had at hand...The wood I have available is called ship's mast black locust, and grows straight and tall, unlike the usual blaak locust which is quite crooked....

In any case, I appreciate your input and will look more deeply into this.