  We demonstrate that the three dimensional incompressible
magneto-hydrodynamics (MHD) system is ill-posed in the largest scaling
invariant space $\dot{B}_{\infty,\infty}^{-1}$. The construction method of
initial data used in this paper is different from the one in a previous work
[DQS] of the author. Specifically, we construct initial data which has finite
energy and is small enough in $H^s\cap \dot{B}_{\infty,\infty}^{-1}$, with
$s<1/2$, such that any Leray-Hopf type of weak solution to the MHD system
starting from this initial data is discontinuous at time $t=0$ in the metric of
$\dot{B}_{\infty,\infty}^{-1}$.
