Update 3: To duplicate this, turn on "Auto code wrapping" in user settings.
It looks like the 'p class="code"' element is being closed prematurely.
<p class="code"></p><div class="codeblock"><tt class="codetext">my $me
+ssage="Hello world\n";<br>
print $message;<br>
</tt></div> <!-- </p> should be here, not before opening <div> -->
That p tag should wrap the entire codeblock.
Either way, thanks for all the work!
Update: This change breaks any css using the .code selector (including the blue web-safe Perl-blue theme).
Update 2: Not necessary any more, demerphq++ fixed it (div became span). "On-site css markup" fix:
p.code { display: none }
div.codeblock {
display: block;
border: 1px solid #666;
color: #069;
padding: 1em;
}