[DisasterDotCom]

So... the root config had an empty cookie prefix, and the core/includes config had "bb" as the cookie prefix. These files have not changed since prior to the upgrade, but I set the root config to also be "bb". I then turned off the no-cache, cleared the system cache, and the problem is still there.

The cookie path is /. The .htaccess file has not changed since August. The only difference between my .htaccess and the one that shipped with 5.1.5 is the rewritebase (my file - /forums/, stock file is just /).

I thought it might also be a memcached thing so I turned off memcache (I assume VB falls back to file based storage then?) but that didn't make a difference either.

The whole thing where refreshing the pages makes the new stuff appear.. has to be a browser caching issue somewhere, but with it being userbase-wide it has to be coming from the server side somewhere.

P.S. There were definitely some changes made to the software that didn't make it into the release notes. I also noticed that the manual sitemap generation required me to put in a new full path to the sitemap location before it would work. There's nothing in the release notes about this change.