For what it's worth, Calibre has been doing this on my computer for some time now as well. I don't use MSE; I use Eset. I used Eset before I started happening....I no longer remember which one, but this started after one of the Calibre updates and hasn't gone away since.
Since I occasionally have issues with Calibre that clear up in later updates, I've just waited and hoped it would go away.
