Mystery solved, retzev - and believe it or not, it goes all the way back to something you did between January 9th and 16th (I could check the access_logs from back then to see when the exact date and time was, but that isn't all that important
). I checked through my backups of the database, and ever since the one I made on January 16th, you've had the option to collapse the header set. Back then apparently the feature only activated with the Variations on Blue theme because it was the only theme that checked to see if the option was set. And apparently things remained that way until recently. Even though the actual button to collapse the header isn't available in Arcane Magic, the theme does check whether or not the feature has been set, and it collapses the header if it has. It's anyone's guess why The Great Orator or possibly even the creator of the BlackDay theme, which was adapted to create AM, wrote the theme that way. Quite obviously it was poor programming. But, sadly, there's often a lot of that going around.
But anyway, what Midnite suggested you do would have worked, but I've taken the liberty of changing the setting in the database for you. The header for Arcane Magic *should* be displaying for you now.