Macbook to Gateway display only works with one account?

I'm using the converter cable to connect my macbook to a gateway monitor in class.
The macbook is open since I don't have a spare apple keyboard laying about so I have to use the keyboard.
But for some odd reason, the display only shows the desktop when using my main working account. When I first power up and the 'log in' screen comes up it only shows the background. It shows up fine on the mac's main display (fortunately) so I can log it, then everything shows up fine.
The same thing happens if I log out of my usual working account and log into the others (admin and test.) They don't show anything but the wallpaper.

It's not an urgent problem as long as it works on the mac's main monitor and the working account is fine. But it is MYSTIFYING . Does anyone know why it's doing this?

 

But it is set on mirror. Same thing on the macbook display and on PC. It's only when I log out and switch to the other accounts it loses it. Would I have to reset it up in each account? Seems odd...