The problem is that only one user is exhibiting your designed
behaviour, Ian, I think.

When users Reply w/Quote to all other users' replies, only the
most recent reply text is appended.

An example:

http://www.anfearrua.ie/ubb/Forum28/HTML/000843.html

Click Reply w/Quote to clareman's post of 19 May 2004 03:55
PM and see.

Click Reply w/Qout to LimerickNomad's post of 19 May 2004
04:00 PM and see the difference.