I actually got a similar problem some months ago,
I just needed one random bow for my lvl 58 hunter, but I only got arrows. When I tried some boxes on amun later, out of 50 boxes i got ~90% arrows and ~10% composite shortbows.
No longbows or normal shortbows. Could be just very bad luck.. but idk :P
I've sent a ticket about this in nov 2012 but no reply still.
