I can duplicate this issue over and over again. I've tried it on several WordPress installations including clean installs.
Step 1: Install WordPress
Step 2: Log in to WordPress
Step 3: Go to: Appearance > Theme Options
Step 4: Set "Color Scheme" to dark and "Default Layout" to content on right.
Step 5: Click the "Save Changes" button
Step 6: Install "Simple Notices" plugin.
Step 7: Activate "Simple Notices" plugin.
Step 8: Go to: Notices > Add New & create a new notice
Step 9: Click on the "Publish" button
Step 10: Navigate to the homepage of the WordPress Site (I.E. http://yourWordPressSite.tld) to see the problem.
Even after your update, it still does not work correctly.
Each time I have verified this issue, it is a basic install of WordPress v3.3.1 with the default 2011 Theme. I do not activate any of the default plugins and I immediately install your plugin. So, with no customization at all, except for your plugin, I'm able to see that your plugin isn't working as it should.