Found this thread about the roll back issue.
Clearing the browser cache, or using a private window does not work.
You have to delete the c:\program data\duplicate folder to get a clean roll back. It seems that the installer will check this folder and install the latest version found here. I guess you could probably delete the subfolder that contains the latest version and that might work. However I did not test that.
Once I deleted the program data\duplicate folder, I reinstalled 2.0.2.1 beta and not longer get the twos complement error.
Also, the idea that this maybe caused by “too fast of a destination” I don’t think that is the case, as I did not have this issue before the latest canary, using the same drives and config files.