I'm using MediaElement.js for a new theme I'm working on. I noticed that it was working fine on my local WordPress installation, running WP 3.9.0, but not on the installation on my server, running 3.9.1. The issue was that the time rail in the player was being displayed as a single pixel wide. When I updated my local installation to 3.9.1, I got the same bug there. I'm running the MediaElement.js function after all other assets have been loaded.
You can see the bug here: http://andersnoren.se/themes/baskerville/my-favorite-beatles-song/ Is this happening for anyone else?