aescripts + aeplugins

Hi everybody, I'm exploiting some of the features provided by rd Scooter, above all I use it to add some offset to keyframes so that I don't have to change their relative position manually. The problem is that when I try to move them backward it happens that the value of the last key frame decreases proportionally and I don't know why! It should stay the same but in a different range of time! Someone can help me understanding what's going on there?