Connect-VIServer only works with a login dialog

I try and connect to my server like so:

     Connect-VIServer 10.95.1.20

A login dialog pops up. I type in "root" and our super secret system password. It connects nicely.

But if I try and connect like this: connect-viserver -server 10.95.1.20 -user "root" -password "OurSuperSecretPassword"

I get this error message:

connect-viserver : 6/4/2015 10:46:03 AM    Connect-VIServer        Cannot complete login due to

an incorrect user name or password.  

and no connection.

What's the story?