  We revisit the question of microcausality violations in quantum field theory
on noncommutative spacetime, taking $O(x)=:\phi\star\phi:(x)$ as a sample
observable. Using methods of the theory of distributions, we precisely describe
the support properties of the commutator [O(x),O(y)] and prove that, in the
case of space-space noncommutativity, it does not vanish at spacelike
separation in the noncommuting directions. However, the matrix elements of this
commutator exhibit a rapid falloff along an arbitrary spacelike direction
irrespective of the type of noncommutativity. We also consider the star
commutator for this observable and show that it fails to vanish even at
spacelike separation in the commuting directions and completely violates
causality. We conclude with a brief discussion about the modified Wightman
functions which are vacuum expectation values of the star products of fields at
different spacetime points.
