Lock security can't set new 4-digit passcode coming from passphrase

[Victor gonzalez]

Story: I can't set directly a 4-pin passcode in unity8-deb on bare metal if there is currently a passphrase security. I need to set swipe(no security) first to get to 4-digit passcode.

Environment:
unity8-deb on zesty

Prerequisite: having a passphrase as security

Steps:

1. Go to Uss>Security&Privacy>Locking&Unlocking>Lock security
2. Set a new 4-digit passcode

Current result: an error appears about a longer password needed
Expected result: changing from passphrase to 4-digit passcode should be posible

Add info: screenshot