Is the 'No Password Required' flag set after you create a user with a non-empty password? - Yes.
Hmm, it looks like a bug. Our QA team will investigate it.
Also - I did try to remove the attribute via the Update User function and the user account control. This selector is disabled for the removal function (not the update).
Ah, of course. Sorry, my bad.
You can do it with the help of a PowerShell script:
$userDN = "%distinguishedName%";
$userDomain = $Context.GetObjectDomain($userDN);
$ADS_UF_PASSWD_NOTREQD = 0x00000020;
$user = Get-AdmUser $userDN -Properties userAccountControl -Server $userDomain
$user.userAccountControl = $user.userAccountControl -band (-bnot($ADS_UF_PASSWD_NOTREQD));
Set-AdmUser $user -Server $userDomain