Why does it matter if a game designer intends for it or not? If it's an improvement on gameplay and well balanced (which it is), then it really shouldn't matter. It's not like a glitch that gives you invincibility, or gives you any significant advantage over other players. The only issue that I can see is that not everybody would know about it, because it wasn't intended, but it's not like it's difficult to figure out.
Regardless, bungie kept flag juggling in every halo (except Reach I believe, but they still threw it in there as an option). So, you honestly can't say that it wasn't intended, otherwise bungie would have kept it out of Halo 3 and Reach completely. I can definitely understand how the announcer can get annoying, but that's an easy fix.