A feature is any unexpected behavior that can be exploited. Being able to have negative values should defiantly qualify for that definition, as you would expect an error.
Although broken collisions are somewhat less exploitable, it should still qualify. Especially from the standpoint of the alternatives.
They are:
Stop the ability to have negative values.
Rewrite it to allow for collision detection in negative values.
Leave it as is, and possibly fix it in some future release.
Given the situation we have for the upcoming 1.0, and the probability that the devs might consider the first alternative easier than the second, I say lets go with the third.