Code in code block macro gets mangled when http:// is included in <a href="..."> tag.

Here's the block of code that I'm including within the "code block" macro. When I go to edit the page with the code block macro in it, then the code shows correctly, but when the page is saved it changes to the mangled version.

Code as it exists when I enter it into the code block and as it displays when I'm in edit mode for the page:
<p>Blah blah blah blah <a href="http://www.blah.com">blah websites</a></p>

Mangled code that appears after page is saved:
<p>Blah blah blah blah <a href=">blahhttp://www.blah.com" websites</a></p>