I just updated to the latest beta (6.5.395) and changed passwords on two sites, and it prompted me to update logins on both sites, but checking the entries afterwards the usernames got messed up, among other things.
On pacsun.com, after changing my password and having 1PW update the login for me, the password was changed correctly, but the username was changed to "Search". On tumblr.com, I changed my password and had 1PW update the login, and my username was changed to "Confirm password" and the password field was blank. All I did on these sites was update my password, no username changes. Haven't tried any other sites yet.
1Password Version: 6.5.395
Extension Version: 188.8.131.52
OS Version: Windows 10
Sync Type: 1PW account