Strange popup in Library that I've never seen before

Doc B

I was looking in my Library to see how many volumes of Pillar I already owned, to see if the discounted set made sense.  I got the following popup, which appeared and disappeared several times...I've never seen it before.  What is going on?

The last time I indexed, everything went fine.  Since this popped up and vanished several times (and at least one more volume popped up in the list when this happened), how do I know if my list is complete?

???

Rosie Perera

This popup comes up when you've edited something like your tags or the name or rating of a book in your library. It has nothing to do with downloading new books into your library. The only reason the list may be incomplete is if you'd typed something into the search box at the top of the library to filter the list, since filtering is based on fields including editable ones like title and tags. As soon as the popup disappears, the catalog has been updated and your filtered list will show everything that matches that search criterion which you have in your library.