md5 of the .exe (or did you mean the .zip the .exe is inside?) of 1.66 is 5f8fdf7e083507a9670261a851725d2f.
The author is changing the version numbers - if you do a binary compare of the two versions, you can see that in the executable:
http://img135.imageshack.us/img135/730/snap058i.png (red text shows the changes)
Because the version number is changed in the executable itself, the md5's are going to be different each time - but the file sizes don't change. That means one of two things:
1. The author is making no changes, except to the version number (ala MuseTips Text Filter).
2. Changes are being made - but then for reasons unknown, the author is packing the code so the binary is always exactly the same size.
I know which one I favour.