How about a workaround?
In my case I took the value of the textarea in a jQuery variable, and changed all "<p> " to <p class="clear"> and clear class to have certain height and margin, as the following example:
jQuery
tinyMCE.triggerSave();
var val = $('textarea').val();
val = val.replace(/<p> /g, '<p class="clear">');
the val is then saved to the database with the new val.
CSS
p.clear{height: 2px; margin-bottom: 3px;}
You can adjust the height & margin as you wish. And since 'p' is a display: block element. it should give you the expected output.
Hope that helps!