I just started experiencing this problem. I've tested it in both Chrome and Safari on OS X and Chrome and Firefox on Windows 7. I've tried disabling all plugins, changing the theme, reinstalling WordPress (via the Update function) to no avail.
My Heading 1 has started appearing bold (ie, as if it were only bold text), as described above. This came out of nowhere, for no apparent reason. What's strange is that this problem only occurs in new posts that I write, or old ones that I update. For example, compare http://www.dheinemann.com/2010/fortnightly-update-28-december-2010/ with http://www.dheinemann.com/2011/fortnightly-update-10-january-2011/.
Looking at the HTML source of these posts, I can see that the newer post contains clean H1 tags, whereas the older post has additional styling applied to it.
<h1>Last fortnight’s goals</h1>
<h2 style="padding-top: 15px; padding-right: 0px; padding-bottom: 5px; padding-left: 0px; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 1.3em; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; margin: 0px; border: 0px initial initial;">Last fortnight’s goal</h2>
The last time I installed a WP update was when 3.0.4 came out, and I haven't installed any new plugins or themes since long before that. I don't understand why it has suddenly changed.
Does anybody know what's going on? Jym, were you able to fix this?