[Phssthpok]

I have an auto-add directory set up for Calibre, and sometimes when I drop files in it they get added, and sometimes not. Previously Kovid has said that this is likely due to files being locked by e.g. anti-virus scanners. However, I just dropped two files in there; one got added, and one didn't. When I opened the directory to look, I found 4 files there, some of which had been there for nearly two weeks. Now, during those two weeks I have rebooted the machine at least three times (Windows update, anti-virus update, and once when Windows went on strike)and restarted Calibre even more often. A quick look with Process Explorer didn't show any processes with handles open for those files.

Can anyone tell me what might be going on here? Why would Calibre be ignoring some files but not others, even across multiple reboots?