I don't know if this is relevant or not, but I tried it three times this morning. The one time the search results were all from the Library, it did not happen. The two times the search results included items from the Inbox and the Library, it did happen.
Anyway, here's what happened when when I opened MB to search results with items from the Inbox and Library:
Then I clicked the menu bar to drag it off screen and pulled it back. It did refresh, but it refreshed to another odd state.
As before, switching to Now Playing or something else made it normal.