Newline removed after loading into Content Editor

Description of bug

Reported in #332629 (comment 687748853)

It seems like loading Markdown into the Content Editor is, in some scenarios, removing extra lines from the page that result in incorrect rendering of tables.

---

contents before saving

* a 

| a | b | c |
|---|---|---|

result before saving

• a

a	b	c

result after saving

• a | a | b | c | |---|---|---|