Disappearing platform problem - RigidBody2D and BoxCollider2D

I've been banging my head against a wall trying to figure t$$anonymous$$s out.

I'm programming a 2D platformer and I am trying to make a platform that disappears and causes the character to fall through. The character has a rigidbody2d and boxcollider2d component and I have a platform set up that reduces its own alpha and eventually disables its boxcollider2d for a period of time after the player touches it.

If the platform has disappeared and the player walks over it, they fall as expected. But if the platform disappears w$$anonymous$$le player is standing on it, the character does not fall through and acts like it is still standing on the platform.

Here is my collision code -

 //When staying in a collision
     void OnCollisionStay2D(Collision2D collision)
     {
         if(collision.collider.tag == "Ground")
         {
             foreach (ContactPoint2D contact in collision.contacts) 
             {
                 if(contact.normal == down) //down = Vector2(0.0f, 1.0f)
                 {
                     ac._isGrounded = true;
                     ac._canJump = true;
                 }
             }
         }
     }
 
     //When exiting a collision
     void OnCollisionExit2D(Collision2D collision)
     {
         if(collision.collider.tag == "Ground") 
         {
             ac._isGrounded = false;
             ac._canJump = false;
         }
     }

Wouldn't disabling the platform's collision box cause OnCollisionExit2D to kick in and change the variables?