Thanks perrin, that was a typo. I modified the code from the original to reduce the number of fields to make it look less cluttered and hence the typo slipped in

The rollback worked when I inserted a tweaked $last_id (i.e. none of the changes to the tables was effected, which is the desired result).

#$last_id = 10;
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However, after I commented the tweaking of $last_id (so the code is back to normal) and called new_account, for some reasons, the changes weren't effected. I had to shut down the MySQL server to get make calling new_account work.

updated

The member_id is defined as AUTO_INCREMENT. With the code as it is (i.e. inserting undef), the member_id is automatically increased.