Doesn't defragment properly

Hey, today I used Defraggler for the first time, and I'm very dissapointed. I analyzed my C drive , and it said it was 50% fragmented. So I clicked 'defragment' (not the quick version). At the start, I checked it every now and then, and it seemed to do well, so I let it run a few hours. After about 3 hours, I came back, and saw it was done defragmenting. But when I then analyzed the drive, it was 45% defragmented! It took hours to defragment 5% of my C drive, and then randomly stopped. I thought maybe I'm unlucky this time, and clicked 'defragment' again. This time, I watched the % fragmentation and the amount of fragmented files closely. After 10 minutes, it said it was 40% done with defragmenting, but the amount of fragmented files was exactly the same as before. Then I clicked 'stop' , followed by 'analyze'. To my surprise, it now said the drive was 54% fragmented!!!! Defraggler not only failed at actually defragmenting, it even (according to the program itself) fragmented some more files. Oh for if you want to know, here's my system:

Acer Aspire 6930G

Intel Core 2 Duo processor T5900

2x 320 GB 5400 RPM hard drives

4 GB DDR2 RAM

GeForce 9600M graphics card

I deinstalled and won't be using it again, but still hope you can fix this for future users, right now they're better off without the program.

What operating system are you using? If it is Windows 7 or Vista the residual fragmentation maybe from System Restore points which cannot be defragmented and the creation of System Restore points during the defrag process which both are know to do. Your lengthy defrag may be because you have very fragmented free space which makes it difficult to place files contiguously and your files are both large and very fragmented.

Have you used other defragmentation software that reduced your fragmentation to more acceptable levels? How can you be sure that it is Defraggler's fault and not the above mentioned problems.