The player controls have totally disappeared now that MediaElement is using a controls.svg sprite (to support retina displays).
I had to add some code to my .htaccess file in order to get them to render in the player again. Hopefully this helps someone else.
AddType image/svg+xml svg svgz
AddEncoding gzip svgz
http://wordpress.org/extend/plugins/media-element-html5-video-and-audio-player/