I wouldn't call it "common", but that's not the first time I've heard of a low strand count 450+ string breaking without warning. I've never heard of that happening with 8125 or Dynaflight '97, but it still makes me leery of tiny strings. An improperly crimped nockset, a small nick, etc. and the string is more liable to break vs. one with more strands in it.
450+ is strong--approximately 155# test per strand--but constant flexing in a single spot could have something to do with it giving. Look at it like bending a wire in the same spot over and over.
Where exactly did it break?
As far as the bow goes, I'd check with Ron--probably get simiar advice as Gordon gave.
Chad