Often when I follow a link that someone has posted I'm not logged in because the link use www and I was logged in on the non-www version of the URL. I suggest that the site owners should decide which URL to use and redirect the other.
I think it's a security thing that subdomains (e.g. www) are independent from each other and the domain.suffix site with no subdomain. Personally I prefer www.domain.suffix, but I have been seeing a lot of sites just go for domain.suffix and redirect to it from www. Either way is the same effort to enforce.
@twicker I noticed this bug before in the past and it has happened again: http://i.imgur.com/R5v78Lf.png
When two people respond at the same time it displays the thread twice. In the My Topics area it is also duplicated and the duplicate is marked as not having been participated in.