In the case of the r/h archer, the cock feather points left (9 o'clock). The rifts are oriented correctly so in case of shaft breakage, the rear part of arrow slides up and over the front part of arrow. Standard procedure for building a woodie.
Now take that same arrow & have a l/h archer nock it on his bow. That cock feather now points right (3 o'clock) and I'm saying that the rift orientation has rotated 180 degrees; a broken arrow shaft will now have the rear part slide under the front part and conceivably into the bow arm or hand.
N.B.! The parallel, horizontal grain in both cases remains parallel, as it should. I'm talking rift/grain-runout here, not the usual parallel grain business.
It's a fine point but it's a safety concern too.
If I'm thinking this through correctly, arrows should thus be made taking into account if the archers are righties or lefties.
Man, I gotta lairn how to post pics & doodles.