Since I am not seeing any problem with url fields on options pages, I can pretty confidently say that it is not ACF. I was trying to give you some things to look at to figure out why you are having this problem.
If you’re game, we can do some debugging to see what’s happening.
Step 1) Open the options page where you are seeing this problem, after the page loads, leave it open in your browser and go on to step 2
Step 2) Open the file /wp-admin/admin.php, the top of the file will look something like this
<?php
/**
* WordPress Administration Bootstrap
*
* @package WordPress
* @subpackage Administration
*/
/**
* In WordPress Administration Screens
*
* @since 2.3.2
*/
After the opening PHP tag and a new line and insert
<?php
echo '<pre>'; print_r($_POST); die;
/**
* WordPress Administration Bootstrap
*
* @package WordPress
* @subpackage Administration
*/
/**
* In WordPress Administration Screens
*
* @since 2.3.2
*/
Step 3) Return to your browser, enter a value that you know is going to cause a redirect in the browser. Click update.
If the problem is something in WP you will see the posted array output. If you get redirected then the redirect is happening before the page is loaded and is happening on the server level before the updated gets to WP.
Do the test and let me know what happens.
