CharacterController.Move() is causing unwanted vertical movement . . . how to fix?

Alright, so the Move() function of the character controller has me stumped. I have a little capsule in my scene and I just wanted to get it moving around, so I wrote the code below. Here's the thing - when I press any two directions (up and right, left and up, etc), the Move() function of the CharacterController starts changing the y values of the character's position. I cannot for the life of me figure out why this is happening. Using transform.position += does not yield the same problem. Any help would be MUCH appreciated.

 using UnityEngine;
 using System.Collections;
 
 [RequireComponent(typeof(CharacterController))]
 public class DummyPlayer : MonoBehaviour {
     
     protected CharacterController myCharacterController;
     
     void Start () {
         myCharacterController = this.GetComponent<CharacterController>();
     }
     
     void Update () {
         ProcessInput();
     }
     
     private void ProcessInput() 
     {
         float analogZ = Input.GetAxis("Vertical");
         float analogX = Input.GetAxis("Horizontal");
         
         Vector3 moveVect = new Vector3(analogX, 0, analogZ); 
         
         if(moveVect.y != 0 || this.transform.forward.y != 0)
         {
             Debug.Log(moveVect.y + " " + this.transform.forward.y); //never called
         }
         
         //this.transform.position += moveVect*Time.deltaTime*40f;
         myCharacterController.Move(moveVect*Time.deltaTime*40f); //why does this affect my y value when the line commented out above doesn't?
         
     }
 }

Also, the variables are named analogX and analogZ because eventually I'd like to get input from a joystick - for now I'm just using the keyboard.

UPDATE:

So after some experimenting around with project settings, I added the following lines to the end of my ProcessInput() function:

 if(myCharacterController.collisionFlags != CollisionFlags.None)
 {
     Debug.Log("I understand nothing anymore.");
 }

then ran the program. When I perform the steps necessary to recreate my original problem, every few updates, I see the Debug statement in the console. Mind you, that aside from the default camera Unity adds when you start a project, I have nothing in the scene except for my childless, parentless capsule. I cannot fathom how it is colliding with itself. Please help!