I’ve never had any problems using WordPress up to 2.8 and TinyMCE-Advanced up to 3.2.4. In WordPress 2.9, single line breaks, whether entered as a shift-enter in Visual or HTML mode or as
in HTML mode are stripped out. I thought at first it was TinyMCE-Advanced 3.2.7, but it breaks whether or not this is activated.
Why does WordPress think it knows better than I how I want my HTML to look? It’s getting worse than Microsoft in this regard.