add_object_page() from admin_menu action: overwrites last menu

[scottconnerly]

When the action admin_menu is fired, I have seen add_object_page() overwrite the last custom post type menu item. $_wp_last_object_menu is supposed to control this, but in this case, it failed.

Custom post types occupied menu positions 26 - 34. then calling add_object_page() at admin_menu overwrote position 34.

Changing the last post type's position to be 40 (so custom post types now occupy positions 26-33, 40), then add_object_page still resides in position 34, and the last post type still resides in 40.

Looking at the code, I can't find the bug myself, would appreciate assistance in pinning down the root cause.

[SergeyBiryukov]

Related: #12718

[SergeyBiryukov]

add_menu_page() should be used instead of add_object_page().

Going to close as duplicate of #23095.