Unpinning Cloth Deforms Object

I have a plane for which I’ve enabled the cloth modifier. I have pinned the four corners of the plane to empty objects. I’ve animated the empty objects to move the plane down and collide with a sphere. (This is all made clear by the video)

I want to unpin the plane once it has collided with the sphere, so I added a vertex weight edit modifier to the plane. This allows me to remove the pinned vertex group when the plane collides.

Everything works as expected except that when the pinned vertex group is removed, the plane remains deformed as if it were still being tugged. In other words, when the plane is unpinned, it doesn’t return to its original shape like a real elastic piece of cloth. Is there any way to achieve this? I’ve attached the blender file below and am using the latest version of blender (2.8).