Thank you for running the experiment.
It is common for a display manufacturer to alter color decoding to compensate for other problems. e.g. To produce a brighter image, they adjust the color temp, which produces a blue image. To try and balance this out, they alter the color decoding, specifically red. People call this red push. Sometimes, especially in sports mode, they also tweak green. They assume that people like to see green grass on a football field.
Usually, but not always, you get proper decoding in the displays "cinema" mode. Sometimes in other modes too. The fact that red is clipped (solid) when contrast is at 12 suggests that there is a decoding error. The only true way to verify is to view a red and geen only mode, which most displays do not include. Samsung added this back in their latest 3D displays. Some displays can be corrected, but it requires going into the service menu and changing the decoder controls. Not all displays include this ability and you need a meter, or red/green only mode to adjust.
The reason I had asked you to look at clipping when contrast is set to 21 is because this is where you set it using the AVS disc. With contrast at 12, and color at 0, does the image seem at all over saturated? When you have a decoding error, the only way to deal with oversaturation is to lower the color control a little bit.
I would not worry to much about red clipping, unless the image seems over saturated. Do people look sunburned? If so, turn color down a few clips to reduce it.
An interesting side note. Soon TVs will prompt you on first startup. They will ask if this is for the home or a showroom floor. The goverment is forcing this. The showroom floor mode, aka torch mode, draws a lot of power and this is part of the plan to reduce power usage.