Sadly, a lot of people don't seem to grasp the concept of a "Thread" of discussion and will post replies as a new thread instead of a reply in the existing thread.
eg: http://www.keil.com/forum/18111/
Therefore my suggestion is to remove the 'Start a Thread' option from within a thread and, possibly, replace it with 'Reply'
Thus it would only be possible to start a new thread from Threads list - and would not be possible to "accidentally" start one instead of replying.