Notice the start of a HTML entity? Looks like it's trying to print > but being cut off by the ellipses.
The thread title is: [SIZE=18pt]<script>alert('hello');</script>[/SIZE]
The function used to chop of the text for previews like this needs to be aware that the text can contain HTML entities (and possibly NCRs) and not chop off the text in the middle of one.
