You have this at the beginning of all your posts:
HTML Code:
<div id="post_message_1208203">
<!-- دعوه لموضوعي -->
<br>
<!--/ دعوه لموضوعي -->
<p align="center"><font size="?4" face="Times New Roman"><font size="4" face="Arial" color="#22229C"><div style=" margin:5px; ">
So if somebody goes to copy/paste the text, it is going to have that font size added in there.