[amagrace]

I got my new Mac and moved everything to it, including Calibre. I put my main book library on local computer for most frequently used books. But I also have a backup library on a USB drive. It worked fine before. After switching to Mac, Mac always complains on ejecting the usb drive, even I closed all apps. After a few experiments, it happens right after I use Calibre to open the external library. The drive can't be ejected even I closed Calibre.

Please help. I don't want to lose any data on the drive by keep force ejecting the drive.
Thanks