Mark: You may be looking at stress concentration, which can cause fatigue and cracking in unexpected places. A couple things could be to blame.
First, there may be some periodic bending of the angle in use. That bending will use the "toe" of the taper as its fulcrum. The result will be work-hardening of the metal until it gets brittle and cracks.
It's also very important to create a true radius at the "toe." A sharp corner will concentrate stress. I have had good luck starting with a rat-tail file, then fine emery cloth wrapped around a 1/4" bolt, and finally buffing with a wheel and compound. The surface of the radius should look like a mirror when you're done.
In tension, there's no question that a Bensen angle end will snap through the hole. At that cross-section, there are only two strips of metal, 1/8" x 1/4" each, to bear the load.
The Gyrobee does not use the Bensen pattern. It employs 1x1 angle with no taper except for a cosmetic one at the very end, past the hole.
Incidentally, Bensen called out 6063-T5, square cornered, for all of his angle braces on the B-8M, except for the engine mounts and the mast-keel braces. Those were 6061-T6 with a corner radius. Probably everything should be.