Markdown rendering does not work for consecutive labels that are inside double quotes
Consecutive labels inside double quotes don't render correctly unless they are separated with a comma. Nothing else works, no period, no other special characters. As you have guessed, even single words within double quotes behave the same. See the following examples.
Consecutive multiword labels
~bug ~"feature proposal" ~"technical debt"
Consecutive multiword labels separated with a comma
~bug ~"feature proposal", ~"technical debt"