When I defrag my 1.5 TB drive (on Win7 x64) Defraggler seems to to a good job (latest version).
But after a loooong time, Defraggler finally reports 100% done... but is still working...somehow.
The file display shows changing files as if Defraggler is working on them but these seem to be a set of about 50 files that rotate and Defraggler never stops.
When I stop manually and check again for fragmentation I get only three files reported. Manually defragmenting per right-click does the job in seconds.
So it seems there is a kind of loop that prevents Defraggler from finishing.
Sorry for not being able to be more specific, hope that helps anyway.