User blog comment:Kirkburn/Technical Update: April 13, 2015/@comment-166269-20150414132240/@comment-166269-20150414133106

Also, clicking the "Compare changes" button in the email prevents at least some keyboard shortcuts from working in Gmail (I only know that  +   doesn't work; I haven't tried others but assume they would be similarly blocked) until you click somewhere else on the page (it doesn't look like the other links cause this).