You’ll need to delete anything that appears in addition to the base URL, such as &feature. Paste and select the URL, then hit the YouTube button. The link should look like this (minus the spaces):
Note: The way I have the YouTube button set up currently, it only works for youtube.com videos, not videos from an international YouTube site. I can likely make a change to allow international YouTube videos to work, too, but YouTube keeps redirecting me back to the base URL whenever I try to look at a video from an international site.
If someone can provide a link to an nice, politically-correct international video, I can make the change!