The inspector is confused by !important CSS rules; it shows the wrong rule as being applied. This cost me a few days of debugging on seekingalpha.com.
Created attachment 97147 [details] Screenshot
Created attachment 97148 [details] Testcase. Inspect the body
<rdar://problem/9608021>
If no one else is looking into this, I'll start putting a patch together.
I'm sorry for overlooking this issue - it sounds like a dupe of the bug 64074 which was fixed in http://trac.webkit.org/changeset/90630. Feel free to reopen this one if the testcase attached still works wrong for you on ToT. *** This bug has been marked as a duplicate of bug 64074 ***
You're right, this is fixed in ToT. Awesome!