Okay try this (quick fix for now):
Edit the newreply.tmpl and find:
<input type="text" name="Subject" maxlength="{$config['subjectlength']}" class="formboxes" size="60" value="$Subject" /><br />
change the part in bold to "hidden" and put $Subject at the end of the tag before the <br .
The same goes for editpost.tmpl, open it and find:
<input type="text" name="Subject" value="$Subject" maxlength="{$config['subjectlength']}" class="formboxes" size="60" />
change the part in bold to "hidden" and put $Subject at the end of the tag.
Hope this helps. Make Backups First!