(Pretty sure this is a Pandoc-Markdown issue, not LP, but it's annoying enough to me that I wouldn't mind fixing it in LP.)
I split my paragraphs into one-sentence-per-line:
Sentence 1.
Sentence 2.
Sentence 3.
I comment out the second sentence:
Sentence 1.
<!-- Sentence 2. -->
Sentence 3.
Now it's formatted as two paragraphs! No good.