On my local version of moodle.org if I go to /my and turn on customizing the following is output.

The block partners does not define the standard capability block/partners:myaddinstance
line 595 of /blocks/moodleblock.class.php: call to debugging()
line 567 of /blocks/moodleblock.class.php: call to block_base->has_add_block_capability()
line 218 of /lib/blocklib.php: call to block_base->user_can_addto()
line 1932 of /lib/blocklib.php: call to block_manager->get_addable_blocks()
line 1025 of /lib/blocklib.php: call to block_add_block_ui()
line 392 of /lib/outputrenderers.php: call to block_manager->ensure_content_created()
line 27 of /theme/moodleorgcleaned/layout/moodleorg/columns2.php: call to core_renderer->standard_head_html()
line 915 of /lib/outputrenderers.php: call to include()
line 845 of /lib/outputrenderers.php: call to core_renderer->render_page_layout()
line 167 of /my/index.php: call to core_renderer->header()

See MDLSITE-3748