I dunno if anyone has reported this yet or not, but it appears that the 'vanishing library items' bug is still around.

I just noticed it when adding an item to my Materials library. The new mat collection didn't appear right away so I collapsed the folder and refreshed it. Item count went from 78 to 35.

Also, just before that happened, I noticed that the delete button disappeared when selecting a mat collection icon but showed up again when I selected a single material icon.