Seems like CharachterController.IsGrounded doesn't work properly

Hello!

I'm trying to make an object with a character controller component have gravity. It thought it would be as simple as this:

Code (CSharp):

1.  
2. using UnityEngine;
3.  
4. public class FPSControllerNOJUMP : MonoBehaviour
5. {
6.     public float moveSpeed;
7.     public bool IsGrounded;
8.     public float currentJumpSpeed;
9.     public CharacterController CC;
10.  
11.     void FixedUpdate()
12.     {
13.         if (CC.isGrounded)
14.             currentJumpSpeed = 0;
15.         if (!CC.isGrounded)
16.             currentJumpSpeed -= 0.1f;
17.         IsGrounded = CC.isGrounded;
18.         CC.Move(new Vector3(Input.GetAxis("Horizontal") * moveSpeed, currentJumpSpeed, Input.GetAxis("Vertical") * moveSpeed));
19.     }
20. }

However, when falls to the ground, it switches between isGrounded and !isGrounded, seemingly randomly. What I'm trying to say is that the object is no longer moving, but isGrounded still changes as it wishes, while the object is still on the ground.

What could cause this in my very simple code?

Thank you!