bark inclusions. Sometime after I wrote that post, I was driving by a native pecan grove and came across this major limb broken out under the weight of a heavy crop of leaves. We did not have a storm to cause this kind of tree damage, but you can plainly see the large bark inclusion at the point of breakage.
In native pecan groves you can find trees that are prone to the development of narrow angled branches and bark inclusions. Given a choice during the tree thinning process, I would remove these future problem makers.