Improperly closing tags inside another tag that starts outside of said tag, creates a huge mess in a phpBB forum. The HTML gets a bit out of whack, and the layout just breaks. This was discovered on 3.0.x, but confirmed to still be an issue on 3.1.x. Some discussion about the issue takes place here: http://forum.zdoom.org/viewtopic.php?f=2&t=52804