Carnster,
I just easily registered on your site. I also was able to logout and log back in without any issues. My guess is that caching was still an issue, which will clear itself up shortly (most browsers will cache for up to 1-day by default). If you still run into issues with different browsers, or the problem persists, definitely let us know what browser and OS you're using, and we can test more.
For the 4.1.1 release (and all future releases), we'll be adding better cache invalidation to prevent this issue going forward.
Thanks,
Alex