When you are tagging in Picard and select an album in the tagged list (right column) you can hit delete to remove the album once it has been completed. This operation unselects the currently select album and removes it. Hitting the down arrow places the selection on the second album in the list (not the first one). Once you only have one album left, there is no way to select it via the keyboard. You instead need to use the mouse (ouch).
Confirmed that it's still happening in 0.16