I view the videos in the browser (stock and Dolphin HD) and both have the same problem. I don't have the same issue with Pornhub for example. I always use desktop browsing mode as I don't like how restricted the mobile versions of the sites are.
I tried to find a more family-friendly example but couldn't. I've tried google to see if others have experienced this issue but all I get is results about how awesome the phone is, so I finally registered here to see if anyone can help find a solution to the problem. I wondered if it was related to the dual-core chip somehow, since my Desire and Hero were single-core and never had these problems.
I'm really hoping the new ICS update will not kill off flash functionality altogether as it is one of the main reasons I got this phone.