mouse pointer dissapearing

sometimes if I just leave, my mouse pointer still for like 2 seconds it will dissapear, If I move it around it comes back. It seems to start when I visit a youtube.com video and scroll over the play/pause button. just leave it on there for like 5 seconds and tell me if your cursor dissapears. Thanks!

ps- I have an optical mouse, IE8 and Vista premium

Happens to me too on YouTube - in Opera at least, I just tried in Chrome as well with no disappearing mouse pointer.
I'm fairly sure this isn't the first time I've seen a mouse pointer turn invisible over eg. Flash and perhaps certain other animated elements in a web page, so I wouldn't be too concerned about it.

Must be a problem on youtube's end