• navigate to /admin/
• turn editing on
• configure the Administration block
• change "Display on page types" to "The current site administration page"
• The block is now hidden from non admin pages (expected)
• configure the Administration block again (from /admin/)
• Option for "Any page" is removed from "Display on page types" and the block is forever lost from non admin pages.

I had to fix this manually by setting pagetypepattern='*' in block_instances table for the settings id

Seems this line is to blame in code: https://github.com/moodle/moodle/blob/MOODLE_29_STABLE/lib/blocklib.php#L1844 because currentcontext and parentcontext are the same.