I dont see the problem either and I looked at a couple of your forums including the one you listed. It is hard to tell what could be wrong, user cache, cookie, who knows.
I would say just removed the old style and stick to one. In the end it will just increase your workload when troubleshooting etc.
You have a very nice forum design, not too heavy. I would stick with the branding you have worked on.
-Jason
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