How I figured out the resolution: by running an AutoIt script on instance startup and logging the values of @DesktopHeight and @DesktopWidth. Why such a strange resolution? It seems backwards and it seems more suitable for a portable device.
The second part of this question also concerns instances running "headless", that is, without any RDP client connected. Once I connect using rdesktop, for instance, it sets the remote desktop to my local desktop's resolution or to the resolution I specify on the command line.
Also, when I connect using rdesktop, the options pertaining to screen resolution on the remote Windows machine appear locked out. I'm not sure if this condition if permanent (guessing there may be a policy setting somewhere), but if it is not, I'd like to know whether the system's settings override the resolution set by the connected client or is it always the other way around.