I haven't seen this behavior on any of my Macs with 11.2, 10.7.3 and the latest version of Safari. Could you follow the document here which details a few troubleshooting steps and instructions on how to report this issue to us?
In an attempt to consolidate numerous threads about video problems with Flash Player 184.108.40.206 I've created a new post where I'd like to have people who are still encountering this issue to either post or link to an existing post with their information.
We're asking for 4 pieces of information
1. A brief explanation of the problem
2. Did disabling hardware acceleration fix the issue
3. A sample URL
4. A copy of your dxdiag report
If you've already provided all 4 answers to us, thank you and please take a minute and copy the URL of your post (right click on the highlighted title of your post as shown in the example screenshot below) and paste it as a reply so your input is not lost.
If you haven't provided these answers, we ask that you take a few minutes and create a new post with the required information.