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Why are array instances changing size relative to each other after using Lock Size button

ZBrush Usage Questions
#1

Here is an array of 3 cubes
Z1

Lock size and lock position button are now on, and I scale my cube. As you can see the location of the cubes stays the same , and the cubes them selves scale down as desired.
Z2 LOCK SIZE ON

Now I un press the lock size button and the size of the cubes change as soon as I unclick the lock size button. Why is this happening ?Z3 SWTCH LOCK SIZE OFF

#2

Some more info I discovered on this is that, even though I am only using the Offset preference for the x , y , z sliders for this array.

What I noticed is when I un press unlock the size button, and I find the anomaly happening mentioned above , if I then switch to Scale instead of Offset to observe the x , y and z slider values, they have changed from their default value of 1.

So maybe some one knows the answer as to why Zbrush is changing the scale values when the lock size button is un pressed there by causing my cubes to scale up along the array?

Thanks