Hi,
I don't think this is a bug, but a problem with your Internet Explorer 9 settings. In Internet Explorer, go to Tools > Developer Tools. Make sure that Browser Mode and Document Mode are set as the same version.
Browser Mode tells the web page what version of Internet Explorer is parsing it. If this says Internet Explorer 9, any CSS (or other code) for lower (buggy) versions of Internet Explorer won't be used.
Document Mode, however, tells Internet Explorer how it should treat the web page. If it treats it as designed for a lower version of Internet Explorer, but doesn't treat itself as that same version, strange things happen.
If you never saw this console before and Internet Explorer is actually shipping with mismatched settings, then this is a bug that needs to be reported to Microsoft. When the settings are mismatched, there is no way to detect it, so there is no way to take it into consideration when coding (although developers shouldn't even have to).