I hope Modman will not mind me stepping in on this one: before the update of the forum, it had only one layout ("style" in phpBB lingo) - the default "prosilver". The few modifications needed for personalization and usability - logo, full-width, and so on - were done directly in the source code. This is not recommended because the modifications would be undone by the next update, unless special care was provided.
So, because there only "prosilver" style existed, everyone's preferences were set to use it. And, of course, after the update it remained like that. But, after the update, the modifications are now done in a child of the default style, called "prosilver-fsb", which is the one set to be used by guests (i.e. not logged-in) and new (post-update) members.
The "old" (before the update) members were seeing the default "prosilver" style. And because no modifications were made to it, even the logo said "phpBB" instead of showing the Freestompboxes logo. This is now fixed, as you can see in the image.
To solve this, we applied a hard fix by setting everyone to the modified style. The problem is that we were now unable to choose a preferred style. Some might like white space and rounded corners. Also, I'm working on a slighly futuristic style that some might like and want to use
SO, to keep the ability to choose a style, I changed the style for everyone to "prosilver-fsb". For reference, this is done by deactivating "prosilver", then reactivating.
I hope that now it is OK for everyone. As always, thank you for your involvement and let us know any issue you might have in using the forum.