[jclient] JMF based CorePlugin VideoMedia causes hang of approx 5 seconds when loaded.

When rendering an xlf with a VideoMedia element, the VideoMedia plugin is correctly loaded - and debug shows that it has opened the video correctly, determined its type and length - but no video plays and other regions on the screen hang with the VideoMedia for approx 5 seconds until the VideoMedia plugin's run() method returns and the next media item for that region is loaded.