I only have a few tags, so there is extra blank space in the tag list box. When I click in this space, it behaves really funny, as if I were selecting an invisible "ghost tag" not assigned to any items. If I click in the blank space, all items in the item list disappear. (I often do this accidentally, it's a bit annoying.) If I click again in the blank space, the items all come back. If I right-click in the blank space I can learn about the "ghost tag". The rename dialog suggests that the name of the ghost tag is all the tags currently in the tag list appended together (e.g. "Need to downloadNeed to read"). The delete option cannot delete the ghost tag. If I right-click and assign the ghost tag a color, it actually appears on the list--I mean, the text "Need to downloadNeed to read" becomes visible--but the blank space still selects the ghost tag too.

This is 5.0-beta.166+e9fd7f2 but I have had this happen ever since I updated (weeks ago), and on multiple windows computers sync'ed to the same library.