Where…
The following files hold the deprecated functions:
~/wp-includes/deprectated.php~/wp-includes/pluggable-deprectated.php- …
Take a look at them and then through their replacement functions, where the calls to _deprecated_function() happen.
Why…
Normally a crash shouldn’t happen. In the “real” PHP world, you’d get an E_DEPRECATED Warning. In WordPress you’ll get a trigger_error() return caused by _deprecated_function() calls. The second trigger_error() argument isn’t used, so it defaults to E_USER_NOTICE and won’t stop your application from running.
How to turn it off…
You can turn this off either by using define( 'WP_DEBUG', false ); or by using a MU-Plugin that sets the filter to false:
<?php
defined('ABSPATH') or exit;
/** Plugin Name: (#105686) Turn off deprecated Warnings */
add_filter( 'deprecated_function_trigger_error', '__return_false' );