Personally, I search for ^p^p and replace with ^p. This is basically required if you see spacing on Word's default setup. If you have tweaked your settings to show spacing on a single carriage return, then you don't need to do this.
Best way to check is to turn on the Paragraph symbols, which is that ¶ symbol. if you see ¶¶ between groups of words, you'll get the double spacing problem. The find and replace I mentioned above, ^p^p with ^p, fixes this issue.
It is really hard programmatically to accept every possible input type and make it correctly output... the editor does a sort of best case of that. We have further filters on the display part of it to make sure that things look right and that the chapter controls work. (contrast, indent, size, etc)