Smart Previews Bug

I found a small bug in the program I think. When I start building smart previews for a wedding, everything looks okay. In the progress bar to the upper left, it shows the current photo it's working on (like 107 out of 3000) or whatever.

However, if I go to smaller folder and begin a second round smart previews at the same time, then both tasks show the same total amount of photos. So the wedding album will start looking weird like "1000 out of 600" as if it's working on 400 extra photos that don't exist hehe. I've attached a screenshot of the issue.