Otto, looking at your pics, it may have been a cold solder joint. I say that based on the bubbles at the interface where it broke loose. Waveski's issue may be the same. A good solder joint will have a real close fit between parts, which makes the joint stronger than a thicker layer of filler material, actually stronger than the filler material only. Machinists will know about how you can stick gauge blocks together without anything but a tiny amount of oil between them. The best joint will have the two pieces clean and flat to within a few thousandths of an inch and the solder wicked into the joint by capillary action.
