http://www.bdsm.com.tw/forum/viewtopic.php?f=3&t=1190 has a reply button near the top which disappears once one has logged in.

Apparently the check if one can reply to a message is only done for logged in users.

So we have the awkward case in which a unlogged in user is presented with a reply button whereas logged in users for this particular item do not get the button!

I'm not saying if the button works or not, I'm just saying it shouldn't be there for non-logged in users in such cases.