Doesn't work for me either, sorry.
It did work for me yesterday, and that's because I used Ctrl+F, which bounced me from video to the root audio view, and I missed that, thinking it had worked.
I should have known it wouldn't work from clicking inside the search field, as the current video view is in force, and the audio and video are both in the same database, therefore, the "All Databases" modifier is totally redundant in this case.
If you're in video and want to search audio, ctrl+F should do the job for you.
You cannot click in the search bar and search for any media type from anywhere in your library. You can create a view scheme that contains all media types and work from there if that's any help at all?
-marko