Run with configured watched not working

[cdjoubert]

Hi,
In the following piece of code, I get an automatic response to sudo if the line with "ctx.config.newvar" is left commented. When it is uncommented, I am still asked for a password. I don't understand why.
My versions :
Fabric 2.4.0
Paramiko 2.4.2
Invoke 1.2.0

@task
def test5(ctx):
    sudo_pass = getpass.getpass("What's your sudo password ? ")
    responder = Responder(
        pattern=r'\[sudo\].*pass.*: *',
        response= sudo_pass + "\n",
        )
    ctx.config.run.watchers.append(responder)
    #ctx.config.newvar = True # sudo won't work if this line is decommented. Why ?
    ctx.run("sudo whoami", pty=True)