Negative Damage Values not applying

If you give yourself an "unbreakable" item using /give (ex. /give Dinnerbone 261 1 -30000) and a negative data value, the item will behave like it was freshly crafted. I've seen it behave like so in both Creative and Survival, with all types of swords, bows, axes, leather armor, and other items. The use of negative damage values worked pre-1.5, so I believe this is relatively new to the game.

(Note: I would have no reason against this except I play a lot of custom maps that revolve around this "feature". Example: Sethbling's TF2 in Minecraft map.)

Thanks!