Image library search failure (plus bonus bug) Answered
Looking back through my images for a picture of a boomerang I made, to attach it to another project, as soon as I went onto the "next" set of thumbnails, I got images that were recent, not tagged with "boomerang".
The first is what I got when I went to the boomerang tag, and is just what I expected.
The second is what I got when I hit "next".
Bonus bug: I couldn't add image notes to these images...
(Using FF 11.0 under XP Home Edition)