Andrew,
I'm certainly not an expert in css, but from what I can gather the <br/> is depreciated and should not be used
http://www.codehelp.co.uk/html/deprecated.html.
I had the same problem you mentioned which I why I suggested it above. It's simple to do a search/replace to replace the <br/> with <div> </div> and that seems to take care of the problem. It's always worked for me with ADE, etc. as a replacement. Bob