Description:
------------
that is actually easy, in main.c :
1991     php_ini_register_extensions(TSRMLS_C);
1992     zend_startup_modules(TSRMLS_C);
1993
1994     /* disable certain classes and functions as requested by php.ini */
1995     php_disable_functions(TSRMLS_C);
1996     php_disable_classes(TSRMLS_C);
1997
1998     /* start Zend extensions */
1999     zend_startup_extensions();
As you can see, zend_extensions are started after php_disable_functions()

That might be a security whole, at list when not documented.