You’re right, this is even documented as so in https://www.gnu.org/software/gettext/manual/html_node/xgettext-Invocation.html:
/* This is the first comment. */
gettext ("foo");
/* This is the second comment: not extracted */
gettext (
"bar");
gettext (
/* This is the third comment. */
"baz");
/* This is the fourth comment. */
So it’s probably broken since 9c19aff7c7561e3a82978a272ecdaad40dda5c00.