Then I noticed that the tooltip that appears when hovering over the blueprint book in the quickbar isn't updated. It isn't showing the new blueprint.
The blueprint book was already in the quickbar before adding the new blueprint.
EDIT:
After looking a bit better this isn't a bug. I was just confused. Apparently, it is possible to link entries in the blueprint library directly with the quickbar. That is what the screenshot is showing. So it makes sense that the tooltip isn't updated...
Would delete this post but I don't have the right to.
