Apparent slow deletion of book/word files from the Recycle Bin?.

I was tidying up my read book files in my Calibre book library and deleted around 850MB. I noticed that the deletion process took around 5mins to complete. I thought that was strange as I have had multi GB files in my Recycle bin many times before which have taken no more than a few seconds to delete. I also make a backup of my Windows on the first of each month and delete the previous months back up which is over 50GB and this only takes a few seconds as well. I am running Win7 with 8GB of RAM and everything else on my PC runs very fast except the deletion of book/word files. Is there a logical reason for this as according to my security scans, Comodo CIS, SAS, MBAM Spywareblaster I have no infections of any kind and other than the above question no reason to believe I am infected?. Thanks in advance for any clarification on this.