Not sure if this is a bug or a feature enhancement suggestion. But when a defrag can actually go backwards, I lean towards 'bug'.
Defraggler 1.16.165. Windows Vista Ultimate, 32-bit, Toshiba Equium 100. 75GB drive with 10GB free space. Lots of big files.
Defraggler defragged my USB drive, 75GB with 35GB free space just fine, including 'Move Large Files to end'. Left a few files undefragged, which then mostly defragged on a second run, but maybe there'd been some internet activity going on.
However, on the main drive, it started with 9GB of fragmented files, 6% fragmentation, and finished with 12GB fragmented files, 18% fragmentation.
I think the effort of trying to move all the large files, in the restricted and fragmented space, was too much for it.
A rerun with 'Move' off left it with just 3 fragmented files, 1.3 MB, 0% fragmentation, so that's good. The Vista defragger ran just three days ago, and left me with the drive in about the 9GB/6% state that Defraggler found it in.
However, it might be good if Defraggler could determine that it was in a case like the above (lots of big files, restricted space) and suggested not using Move, or even declared it would run without it.
Unless you think Defraggler's techniques are such that it ought to work anyway?