Appearently WP chaches the search results within the media results. I could not find a way to clear this cache, and it turns out to be quite annoying.
I have a large site with a few houndred images in the media library. In the 'Insert media' dialog, I start looking for some images by typing in the search phrase in the search box at the right top corner. If there are no results, I know I have to upload those images.
So I upload them. Putting in the search terms again still does not find the images just uploaded although the filenames match the search terms. I then have to use different search terms to find these images.
1) In the 'Insert media' uploader, I search for "wordpress". No results.
2) I upload the images 'wordpress-screenshot-1.jpg', 'wordpress-screenshot-2.jpg' and 'wordpress-screenshot-3.jpg'.
3) In the 'Insert media' uploader, I search again for "wordpress". No results. I then search for "screenshot" - the 3 files are found. I search for "press" - also works.
By the looks of it the query results get cached somewhere. I tried to find out where - but no luck.
Any help appreciated!