One more thing... I recommend that the password must be asked 2 times, to validate that we didn't pushed the wrong key...

Done :-)
I get the same issue. I cant even change ssh password. It says its done buy still old one in place. The only thing I have changed was sd card on my Pi. Didn't have this issue on my other card so that my be it. Will try it and report back.
ssh password and webUI password are independent. Both are default minepeon/peon
Change ssh password: ssh into pi and use
passwdReset webUI password to default: ssh into pi and do
echo 'minepeon:$apr1$DcY4Nshh$qoM20SzA2h2tBKyKUuAsg/' >opt/minepeon/etc/uipassword