In Blog tab, turn editing on. Then delete the two blocks. Turn editing off. Then turn editing back on. Instead of a Blocks menu (which I expected to see), I get the following error:
Notice: Use of undefined constant PAGE_MY_MOODLE - assumed 'PAGE_MY_MOODLE' in /var/www/html/demo/lib/blocklib.php on line 347
and it is impossible to restore either of the blocks.