I do not have a fix unfortunately, but must mention this happens to me too on both my own workhorse AND on BRAND NEW BUILT AND VISTA CLEANLY LOADED PCs we build for our customers.
As an example I have a PC sitting next to me cleanly built that has been running overnight (more than 12 hours) and is still only 43% defragmented. This machine has bugger all on it too of course being cleanly built. I've only been using Defraggler after loving CCCleaner for years for a few weeks, but I'm not inspired by confidence at the moment.
