Commented Feature: "+" gets disabled for unknown reasons randomly [4717]

Sometimes "+" is disabled for some reason and the only way to make it possible to add new entry again is to restart VS. Pretty annoying.
VS 2015 Update 5, Windows 8 Pro.
Comments: ** Comment from web user: alexandis **

I'm not sure attach file has been attached. It told me I'm going to leave the page, when I pressed submit after attaching png...