In Blender 2.7, there seems to be a problem with copying a shape key. The copied key does the negative of the original key.
I first establish a basis shape key, then Key 1.
Next I edit an object in Key 1, then add a Key 2. In order to make Key 2 do the same distortion as Key 1, I go to the box below “blend” and identify Key 1 as the “shape used as a relative key”,
Then when I change the value of Key 2, I get the negative of the effect of Key 1. Looks like there’s a minus sign that shows up when I try to copy key 1 to Key 2.
Am I doing something wrong, or is this a bug?