[...]
Whatever "it works" really means. Without seeing example entries and their pwdChangedTime values it's impossible to say anything meaningful - except the usual "it works for me".
it turns out this malfunctioning is affecting only entries whose password has been changed last time before the upgrade [1].
So to be sure that 'it works for you' you should pick a pretty old entry and craft the range pwdChangedTime query accordingly.
And of course this applies to you only if you did a in-place update. If you slapcat-ed and slapadd-ed your entries, you are pretty safe,
regards,
Francesco
[1] a fresh ldappasswd or a modify on the pwdChangedTime attribute fixes the issue on a given entry.