Setting UI elements active while the mouse is already over them -- how to detect?

I have UI buttons that I set from active to inactive and vice versa. If the mouse cursor is over a button when the button is set active, then Unity does not immediately detect that the mouse is over the button. What is the best way to get around this?

I should also note that keeping the UI invisible instead of inactive isn’t going to help me in this case. The position of the buttons are subject to change, and repositioning a button to underneath the mouse also results in the mouse not being detected.

Don’t know if it’s what you want but this will check the mouse point and return all the UI elements a Raycast passes through. The Text of the button will be the top one:

using UnityEngine;
using UnityEngine.EventSystems;
using System.Collections;
using System.Collections.Generic;

public class RaycastUI : MonoBehaviour {

	public void RayCastingToUI ()
		PointerEventData PED = new PointerEventData(EventSystem.current);
		PED.position =  Input.mousePosition;

		List<RaycastResult> HITS = new List<RaycastResult>();
		EventSystem.current.RaycastAll( PED, HITS );

		foreach(RaycastResult hit in HITS)
			GameObject go = hit.gameObject;
			Debug.Log ( + " how many hit = " + HITS.Count);