"Create collection" fails as already existing, but the collection is nowhere in the list

I created a collection in the v3 web UI, then couldn't find it anywhere in the collections list, so I assumed it hadn't been created and tried again with the same name. The second attempt errors out.

Resolution: The first create actually succeeded -- empty collections are not rendered in the collections list, so a brand new collection with no books in it is invisible, and the retry then legitimately fails on the duplicate name. Add a book to the collection from the book's detail page and it appears immediately. The same rule makes an empty collection awkward to remove: you may have to put a book into it before you can select and delete it. (Deleting a collection from the sidebar was separately broken in early v3 betas and fixed in a later build.)