Cancel the bubble when mentioning user

Please check here if you can cancel the username autocomplete bubble once you start typing @ + letter - there is some bug - I am forced to select any userName to just close the bubble - clicking outside the bubble or Esc key popup doesnt close the bubble/popup. The only way is to delele all text with the user name + @

Note: you can even open some other post edit mode and the bubble/popup window with prepopulated username doesnt go away.