Trying to get property of non-object in …/capabilities.php on line 1112

Hi there,

I have started getting the following warnings in debug.log.

The steps to reproduce:

1. Create a custom post type with a plugin.
2. Open wp-admin/post.php (the post editing page) of the post type.
3. Leave the page open and disable the plugin.
4. Wait for admin-ajax.php causes the warnings.

[20-Jul-2014 12:27:30] PHP Notice:  Trying to get property of non-object in ...wp-includes\capabilities.php on line 1112
[20-Jul-2014 12:27:30] PHP Stack trace:
[20-Jul-2014 12:27:30] PHP   1. {main}() ...wp-admin\admin-ajax.php:0
[20-Jul-2014 12:27:30] PHP   2. do_action() ...wp-admin\admin-ajax.php:82
[20-Jul-2014 12:27:30] PHP   3. call_user_func_array() ...wp-includes\plugin.php:470
[20-Jul-2014 12:27:30] PHP   4. wp_ajax_heartbeat() ...wp-includes\plugin.php:0
[20-Jul-2014 12:27:30] PHP   5. apply_filters() ...wp-admin\includes\ajax-actions.php:2130
[20-Jul-2014 12:27:30] PHP   6. call_user_func_array() ...wp-includes\plugin.php:192
[20-Jul-2014 12:27:30] PHP   7. wp_refresh_post_lock() ...wp-includes\plugin.php:0
[20-Jul-2014 12:27:30] PHP   8. current_user_can() ...wp-admin\includes\misc.php:723
[20-Jul-2014 12:27:30] PHP   9. call_user_func_array() ...wp-includes\capabilities.php:1337
[20-Jul-2014 12:27:30] PHP  10. WP_User->has_cap() ...wp-includes\capabilities.php:0
[20-Jul-2014 12:27:30] PHP  11. call_user_func_array() ...wp-includes\capabilities.php:956
[20-Jul-2014 12:27:30] PHP  12. map_meta_cap() ...wp-includes\capabilities.php:0
[20-Jul-2014 12:27:30] PHP Notice:  Trying to get property of non-object in ...wp-includes\capabilities.php on line 1113
[20-Jul-2014 12:27:30] PHP Stack trace:
[20-Jul-2014 12:27:30] PHP   1. {main}() ...wp-admin\admin-ajax.php:0
[20-Jul-2014 12:27:30] PHP   2. do_action() ...wp-admin\admin-ajax.php:82
[20-Jul-2014 12:27:30] PHP   3. call_user_func_array() ...wp-includes\plugin.php:470
[20-Jul-2014 12:27:30] PHP   4. wp_ajax_heartbeat() ...wp-includes\plugin.php:0
[20-Jul-2014 12:27:30] PHP   5. apply_filters() ...wp-admin\includes\ajax-actions.php:2130
[20-Jul-2014 12:27:30] PHP   6. call_user_func_array() ...wp-includes\plugin.php:192
[20-Jul-2014 12:27:30] PHP   7. wp_refresh_post_lock() ...wp-includes\plugin.php:0
[20-Jul-2014 12:27:30] PHP   8. current_user_can() ...wp-admin\includes\misc.php:723
[20-Jul-2014 12:27:30] PHP   9. call_user_func_array() ...wp-includes\capabilities.php:1337
[20-Jul-2014 12:27:30] PHP  10. WP_User->has_cap() ...wp-includes\capabilities.php:0
[20-Jul-2014 12:27:30] PHP  11. call_user_func_array() ...wp-includes\capabilities.php:956
[20-Jul-2014 12:27:30] PHP  12. map_meta_cap() ...wp-includes\capabilities.php:0
[20-Jul-2014 12:27:30] PHP Notice:  Trying to get property of non-object in ...wp-includes\capabilities.php on line 1113
[20-Jul-2014 12:27:30] PHP Stack trace:
[20-Jul-2014 12:27:30] PHP   1. {main}() ...wp-admin\admin-ajax.php:0
[20-Jul-2014 12:27:30] PHP   2. do_action() ...wp-admin\admin-ajax.php:82
[20-Jul-2014 12:27:30] PHP   3. call_user_func_array() ...wp-includes\plugin.php:470
[20-Jul-2014 12:27:30] PHP   4. wp_ajax_heartbeat() ...wp-includes\plugin.php:0
[20-Jul-2014 12:27:30] PHP   5. apply_filters() ...wp-admin\includes\ajax-actions.php:2130
[20-Jul-2014 12:27:30] PHP   6. call_user_func_array() ...wp-includes\plugin.php:192
[20-Jul-2014 12:27:30] PHP   7. wp_refresh_post_lock() ...wp-includes\plugin.php:0
[20-Jul-2014 12:27:30] PHP   8. current_user_can() ...wp-admin\includes\misc.php:723
[20-Jul-2014 12:27:30] PHP   9. call_user_func_array() ...wp-includes\capabilities.php:1337
[20-Jul-2014 12:27:30] PHP  10. WP_User->has_cap() ...wp-includes\capabilities.php:0
[20-Jul-2014 12:27:30] PHP  11. call_user_func_array() ...wp-includes\capabilities.php:956
[20-Jul-2014 12:27:30] PHP  12. map_meta_cap() ...wp-includes\capabilities.php:0
[20-Jul-2014 12:27:30] PHP Notice:  Trying to get property of non-object in ...wp-includes\capabilities.php on line 1116
[20-Jul-2014 12:27:30] PHP Stack trace:
[20-Jul-2014 12:27:30] PHP   1. {main}() ...wp-admin\admin-ajax.php:0
[20-Jul-2014 12:27:30] PHP   2. do_action() ...wp-admin\admin-ajax.php:82
[20-Jul-2014 12:27:30] PHP   3. call_user_func_array() ...wp-includes\plugin.php:470
[20-Jul-2014 12:27:30] PHP   4. wp_ajax_heartbeat() ...wp-includes\plugin.php:0
[20-Jul-2014 12:27:30] PHP   5. apply_filters() ...wp-admin\includes\ajax-actions.php:2130
[20-Jul-2014 12:27:30] PHP   6. call_user_func_array() ...wp-includes\plugin.php:192
[20-Jul-2014 12:27:30] PHP   7. wp_refresh_post_lock() ...wp-includes\plugin.php:0
[20-Jul-2014 12:27:30] PHP   8. current_user_can() ...wp-admin\includes\misc.php:723
[20-Jul-2014 12:27:30] PHP   9. call_user_func_array() ...wp-includes\capabilities.php:1337
[20-Jul-2014 12:27:30] PHP  10. WP_User->has_cap() ...wp-includes\capabilities.php:0
[20-Jul-2014 12:27:30] PHP  11. call_user_func_array() ...wp-includes\capabilities.php:956
[20-Jul-2014 12:27:30] PHP  12. map_meta_cap() ...wp-includes\capabilities.php:0

I looked into the core and this is the part causing the warnings.

$post_type = get_post_type_object( $post->post_type );

		if ( ! $post_type->map_meta_cap ) {

Simple checking of is_object( $post_type ) would prevent such an issue.

Could somebody confirm this problem? Thanks.