How to get consistent screen resolution?

[Chris G]

I have a system using a big TV as its screen and it doesn't always
come up at the correct resolution.  I can't see any rhyme or reason as
to when it gets it right and when it doesn't.

The 'correct' resolution is 1920x1080 but it sometimes comes up at a
'non-widescreen' resolution of 1600x1200 or similar.

Can anyone suggest why this might be happening?

The DDC detection in Xorg.0.log shows the resolution I want to use but
it doesn't appear in the display settings applet.

-- 
Chris Green