Why does it do it?

This paragraph spacing issue is doing my head in, why does it do it? You have your post looking all pretty then upload it and and wham, bye bye paragraphs. And not consistently either!

No amount of editing will fix it, and with the post below I completely re wrote it and the good para spacing swapped from top to bottom.

Grrrr, humph, don't they know I'm anal about grammar and layout.