When using the rich editor, wordpress alters the HTML on save, particularly replacing paragraph marks with double newlines. Why does it do this? It's unnecessary, as wpautop deals with text with paragraph tags in fine, indeed it's harmful, as TinyMCE knows the structure of what you're writing better than wpautop does, so is more likely to produce valid HTML (in particular, wpautop sometimes gets confused about whether it needs p tags in blockquotes).
Is there a reason for this (mis)feature? If not, hopefully it can be removed in future versions.