After an Active Directory fail RDP connection started to ask for credentials twice (once on local RDP program, second time on remote's logon screen)

I already looked at Windows 2008 R2 RDS - Double Login Solution provided there doesn't work for me.

The server is alone, without AD/DNS services, RDP service isn't installed I tried every security settings on RDP-Tcp (RDP, Negotiate, SLL)

Logon option is set to "Use credentials from the client"

Both windows client and server use RDP 7.1

fPromptForPassword regitries are set to 0

Local Computer Policy\Administrative Templates\Windows Components\Remote Desktop Services\Remote Desktop Session Host\Security\Always prompt for password upon connection is set to "Disabled"

Why i am sure the problem comes from the server and not the client ? This problem affected a 3rd RDP program on Android too (it was directly showing "preparing desktop previously, on both MS RDP and the 3rd program)

No bakcup are available (Else the Active Directory wouldn't be a fail, but just a lose of time)

I am wondering if a rule linked to RDP got changed after the AD install+unistall, but i'm unable to find where.

While this is not a critic problem, this is very annoying.

I don't know if more information are needed, if it's the case and if you are patient enough, please tell me what is missing and i'll edit this post to add the missing informations.