I also vaguely remember that including a blank line in between paragraphs keeps the text of paragraphs from being merged. I certainly hope that functionality has not changed. Mashing together paragraphs would make the reviews more difficult to read.
I'm just following up here to confirm that the display is working as designed. Currently single, double, and triple new lines in Plot Summaries will be stripped, as we are no longer allowing paragraph breaks for summaries. This display is intentional, so you won't be able to add paragraph breaks in this data section.