In HTML, elements containing nothing but normal whitespace characters are considered empty. A paragraph that contains just a normal space character will have zero height. A non-breaking space is a special kind of whitespace character that isn't considered to be insignificant, so it can be used as content for a non-empty paragraph.
Even if you consider CSS margins on paragraphs, since an "empty" paragraph has zero height, its vertical margins will collapse. This causes it to have no height and no margins, making it appear as if it were never there at all.
If I understand your issue this should work
&emsp—the em space; this should be a very wide space, typically as much as four real spaces. &ensp—the en space; this should be a somewhat wide space, roughly two regular spaces. &thinsp—this will be a narrow space, even more narrow than a regular space.
Sources: http://hea-www.harvard.edu/~fine/Tech/html-sentences.html
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!
Source: Stackoverflow.com