HTML comment block is read back as an inline HTML macro merged into the previous paragraph in CommonMark Markdown 1.2

When reading markdown/1.2 content containing an HTML comment block after a paragraph, e.g.:

x

<!--
a

b
-->

Expected: the comment is read back as a standalone html macro, separate from the paragraph.
Actual: it's read back as an inline html macro, and rendering the result again gives

x<!-- a  b -->

in the same paragraph.