it's a known issue, currently under investigation by the Devs (pretty sure, or am I thinking of the Chrome issue ).
none the less, the Dev guys will see this and look into it.
meanwhile, reverting to the previous version will side-step the issue or, what I've always done because any defrag takes way too long and defrags stuff that has little impact on performance, is to go to the File List tab, hit Analyse, sort the Size column into Descending order, group select the files >50k and click Defrag Highlighted.
repeat for the Fragments column and just select the files > 20 fragments.
that way you only defrag the worse offenders. anything else will then be either small enough or not fragmented enough to be of any great concern.
and it only takes mere minutes for the greatest performance hit.
I recently upgraded to the professional package to find the same problem that I had with the free version, not defragging . I used the suggested method by MTA and it works. Just few files at the time starting with low file size.
Thanks for the suggestion and I hope that bug will be fixed soon.