I just did this too, and the same thing happened. Analysis showed my D partition was 100% defragged with no files in the fragmented list. I pressed defrag again expecting it to not move anything and finish immediately. An hour later, it's still moving things around. Obviously the 'optimum layout' that the algorithm makes during analysis is not definitively optimum!
I think I probably have the wrong idea about defragging though. I have two programs that my laptop struggles to run smoothly (Eg Space Engine), and one of the bottlenecks is reading from the disk fast enough. What I hoped defragging would do is put all the files pertaining to those programs right next to each other on the disk. Instead, defragging a disk seems to be more about trying to get each file wholly into one cluster (as opposed to spanning clusters), without any real attempt to optimise by collating related data.
If I want all the Space Engine files all to be put contiguously/adjacently in the same area of the disk, would the 'defrag folder' option do that?
I'm trying it right now, but it's taking a VERY long time - 6 fragmented files in 17 total fragments has taken over two hours, and I've still got 2 fragmented files in 5 fragments to go.
Thanks.