When I saw that the new L5 library allows you to filter the library to 'open books' of course I had to try it. 82 books open!!
Next I timed opening an 82 book layout (5 languages and who knows how many fonts): 30 seconds!
Next, I decided to time opening a 20 book layout. Probably faster than I could blink my eyes!! And maybe so:
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No need for a 'bug' report unless someone else does this too.