just a quick heads-up to all of those who had to deal with this unfortunate bug:
Set-ADAccountPassword -Identity $User -NewPassword $Password -Whatif
Sets the password anyway. I checked by looking at the passwordlastset attribute of the user and found it had been reset.
It’s going to be fixed with Server 2016 according to Microsoft:
This is fixed in Windows Server 2016 and the accompanying RSAT.