Running WordPress with Yii framework sub-site.
Use of is_a() function in capabilities.php (line 486) is causing errors, since causes instantiation of a WP_User object - which is unknown to Yii.
is_a() was deprecated in PHP 5.0.0 - but did not cause this problem until PHP 5.3.7, when its behaviour changed: if first argument is not an object, __autoload() is triggered. (see php manual)
Example: error if I use get_users() with the 'all_with_meta' option.
This is at least inefficient - and in my situation fatal! Even when it works, this generates unnecessary log warnings in many cases (see all the other posts)
if ( is_a( $id, 'WP_User' ) )
if ( $id instanceof WP_User )
Please can you fix this for increased compatibility in future versions - both with PHP and all the other plugins!