This is odd. I see the following markup (with a few line breaks added inside of tags to make it easier to read:
<p class="code"><div class='codeblock'><tt class='codetext'><font size +="-1">my $message="Hello world\n";<br /> print $message;<br /> </font></tt></div><font size='-1'><div class='embed-code-dl' ><a href="?part=1;abspart=1;displaytype=displaycode;node_id=487248" >[download]</a></div></font></p>
I thought it might be a glitch in the HTML cleaning code we have, but it doesn't appear to be so. Likewise I've inspected the code and I dont see how the html youv'e posted could be generated. Since I can't repeat the bug I'm not sure how to proceed with this.
What browser are you using?
Update: I've worked it out. The problem was nesting a div inside of a p is apparently illegal, so if you had CSS keyed on the p tag it would show up as _though_ it was an empty p block even thought it wasnt really. Ive changed things so that when p tags are used the internal sections are spans and not divs. From what i can tell this sorts it all out. I also checked the Perl-Blue scheme and it seems to look fine.