Manual Absolute Effect vs Relative Effect over Submaster

I can't find any posts/replies from ETC/Moderators explaining why this doesn't work, or just that it doesn't work. I found one related post from   two months ago but they didn't get a reply. 

When I have a Submaster controlling the Intensity of a Channel, and then I manually apply a Relative Effect to that channel it runs as expected using the value from the Submaster as the Background from which the effect scales. However this doesn't work for Absolute Effects when using Action 1=Background Action 2=0.

What is the difference, why does it work for Relative but not Absolute?

Thanks,

Steven

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