Q: Photo thumbnail behaviour when adding photos to a page within a book project

So I created a book project to make a book of my most recent holiday. I make one every year but this is the first one using Photos. I dragged in all my photos into the project – about 1200.

I'm really struggling to figure out the behaviour of the photo strip below the book project window. Most of the time when I place a photo into the book the thumbnail strip will automatically scroll L-R all the way back to the first photo in the project. This behaviour is highly frustrating as it means I then have to scroll all the way back to where I was in the sequence. Creating a book has become a huge chore as a result. Sometimes it doesn't do the scrolling and remains in place when I drag in a photo – this is the behaviour I want all the time but I have no idea why it happens or how to make this the default behaviour.

Photos seems to automatically pre-select some photos in the thumbnail strip based on the number of slots available on the displayed pages - and it scrolls about while doing that. Maybe it has something to do with this.

Anyone else having this problem or can explain the behaviour?