I've done this a few times, but not over VGA or HDMI... typically over the Svideo out.
Hook it up, press your Function-key for switching the current monitor until the TV displays
the computer. Then use either the Intel/ATI/nVidia graphics control panel to tweak settings for
dual monitor support, which should have refresh rates and etc in there.
Sounds to me like it fired up outputting a signal to all ports, and then went back to the default monitor
when Windows had loaded enough drivers.
Granted it has a Intel chipset for graphics (hah) but I took a broken laptop from dell and shoved it in my media cabinet
and forced it via settings and BIOS to always start with the external monitor. Added a bluetooth keyboard and had a HTPC.
Toshiba, if I remember the one I just sold, also has a F key for the monitor switching.l Looks like two boxes next to each other usually.