Have a few representative freehanded circles that will no doubt explain the issue in fully without further need for words.
What? You're so completely disconnected by the collective freehanded-circle mindhive to require words to have meaning conveyed to you? Poor you. Here, let me try and explain with those imperfect tools called words.
Now this isn't a particularly grave problem as:
- It only works on sites that do expand Youtube links to the embedded player in the first place (AFAIK, that's just Gaming and SU)
- The embedded YouTube player feature is rather hidden
...but it still is most likely a bug rather than a feature.