Hi,
I must admit i was surprised the first time i used messaging with Moodle 3.2 (and Boost theme, on moodle.org), with my message sent just after "Hi," (then "return").
And option would be cool. Or at least a message (when overiding ?) explaining the Return and Ctrl + Return things, that could be really helpful.
But as Gareth said, i don't think it's really a theme related issue...