Strange line of code appearing in my "Quick reply"

Here's an image of it:

I went into my post.php and ctrl+f'd that line.  I then deleted that line, saved, and uploaded the new post.php but nothing changed; the line of code still appeared.

Are there any other files that I should check that might be the source of this problem?  I really don't want it to show >.>

Incase it's a syntax error, here's a snippet of code from around it.

$form = '<form id="post" method="post" action="post.php?action=post&tid='.$tid.'" onsubmit="this.submit.disabled=true;if(process_form(this)){return true;}else{this.submit.disabled=false;return false;}">';

    // If a quote-id was specified in the url.