I haven't ever seen one break here before, but the implications are fairly serious. A search through my pile shows two different construction techniques - this style - apparently spot welded and polished, and what I presume is a later style with a through bolt with a wide head on the inside of the holder. Of course, you can't really tell unless you pull the shoes, which is a major pain...

a little public service reminder, as if you don't already have enough to worry about.