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Constructed plane creates with -1 Z vector points have +1 Z vector

So i am programming parts and when I create and measure my manual alignment points the vector of those points are positive in the Z axis. When i construct a plane using those points the vector of the plane is the exact opposite. I have had this issue very rarely in the past but for some reason its every part from a new customer (34 part numbers). Could it be CAD related? or is it something else?

Its not an issue because i know how to fix it but i want to know why its doing it. Any ideas?