Seriously, what Miniduffa said. Every time the World of Tanks ad appears in the rectangle ad box during a video, it shifts the video to the right. Any part of the video that is off to the right will now be off the screen and unseeable. Making the video fullscreen will sometimes make the video centered again (until you leave fullscreen again, in which state the video is still off-center), or in some cases it will move the video further to the right and off-screen.
This is seriously annoying, and renders some videos un-watchable. This has been happening on any youtube video with a World Of Tanks ad appearing on it for at least a couple months now if not longer. Please fix this soon.