Virial ratio behaviour
The ratio $T/\Omega$ tells you about the acceleration of the system - or more specifically, the second derivative of its moment of inertia - it does not tell you about the velocity.
If the system collapses because it has $T/\Omega&lt;0.5$, then when it reaches $T/\Omega=0.5$ it stops accelerating. That doesn't mean it stops collapsing. It overshoots in the same way that if you compress a spring it goes beyond the equilibrium position before bouncing back once the deceleration becomes large.
NB: I answered the question (of which your question is a subset) that you linked to in the same way.