Videos appear zoomed in
Just recently, Safari has started showing videos zoomed in. For example, on the BBC Weather site, if I click on the UK forcast I just get the presenter's chest. If I double-click on it I get it full screen, and it's fine, but if I press [esc] it goes back to being zoomed in in its box.
If I try to watch videos that allow you to re-size the box that the video is in, re-sizing the box cures the problem.
I'm on a Retina MacBook Pro, sporting OS X 10.8.2, with Safari Version 6.0.2 (8536.26.17). I have also installed the WebKit and it has the same problem. I have WebKit Version 6.0.2 (8536.26.17, 537+)
YouTube is fine, though.
Have I done something by mistake to make this happen?
MacBook Pro (Retina, Mid 2012), OS X Mountain Lion (10.8.2)