Strange TI2009 Image MD5 issue

I was checking images created by ATI2009 (9709) although build version probably has no bearing on this.

Scenario:

Using ATI Boot/rescue disk.

1) Create Image of say a 10GB partition

2) NO compression

3) Full backup

4) Image saved to another partition

5) Validate Image

6) Immediately repeat the above (obviously renaming the images so that they are individual)

7) Compare the two resultant "Identical images" and they are the same size.

8) Create MD5 hash values for each of the image files and they are different.

If i try creating multiple images of the same partition using the rescue disk one after the other so nothing changes, I get the same resultant sized image files as one would expect, but they have all been created differently, as an MD5 creation and compare indicates - why?

The actual backed up data is accurately backed up, but I'm curious as to why ATI2009 creates an image file differently upon each creation of the exact same source data.