Hmmm.. haven't seen that before.
Is that quoting an Older post (made under an older version)?
The reason I ask is that threads doesn't use <br> anymore, as it's not XHTML compliant. The last several versions of threads have used <br />.
The only time I ever see the <BR> pop up is when I go and edit a version 6.0 or before post... as those were created with the older tags. The markup stuff was all changed around in one of the early version 6 releases.
See if you get the same thing when you quote a post made under a current version.
If you need to, Bug reports go at Infopop.com .... so that they can properly track and fix them.
http://community.infopop.net/2/OpenTopic?a=cfrm&s=729094322&f=8233088913 
