Luminance values change after rendering

Hi there,

I am currently editing some footage in CS5.5 that needs to be broadcast safe.  I've been going through the shots using the YC scope and pulling down the luminance values where they are peaking over 1.0.  When I go to render the shots the luminance levels jump back up to over 1.0.

Can anyone tell me why this is and what I need to do to correct it.

Thanks