After seeing this answer from Jeff, I realized that the shiny new userscripts I installed recently might have something to do with the problem. Testing revealed that the WMD keyboard shortcut disabler was the culprit.
Time to work on getting the same functionality without forcing me to constantly prove my humanity.
An updated Chrome user script based on Rob's (linked above):
// ==UserScript==
// @name Cya WMD shortcuts
// @namespace Rob W
// @version 1.0
// @run-at document-end
// @description A hook to disable WMD keyboard shortcuts
// @match http://stackoverflow.com/*
// @match http://meta.stackoverflow.com/*
// @match http://superuser.com/*
// @match http://meta.superuser.com/*
// @match http://serverfault.com/*
// @match http://meta.serverfault.com/*
// @match http://askubuntu.com/*
// @match http://meta.askubuntu.com/*
// @match http://answers.onstartups.com/*
// @match http://meta.answers.onstartups.com/*
// @match http://stackapps.com/*
// @match http://*.stackexchange.com/*
// @exclude http://chat.stackexchange.com/*
// @exclude http://chat.*.stackexchange.com/*
// @exclude http://api.*.stackexchange.com/*
// @exclude http://data.stackexchange.com/*
// @exclude http://*/reputation
// ==/UserScript==
(function() {
var p = document.getElementById('wmd-input').parentNode;
function ignore(e){e.metaKey && e.stopPropagation();}
p.addEventListener('keydown', ignore, true);
p.addEventListener('keypress', ignore, true);
p.addEventListener('keyup', ignore, true);
}()
);
Rather than eating all keyboard events, this only prevent Markdown from seeing command+whatever events.