Comment 5 for bug 1313748

The default printer bit was not included in the Bonjour broadcasts intentionally as it can get confusing if there is more than one server advertising printers.

See https://www.cups.org/str.php?L4412.

What you can do is marking any printer, the ones discovered by cups-browsed included, as default printer. As cups-browsed does not remove the local default printer when it shuts down (or when the printer disappears), the default setting once done stays conserved until changed.

Closing as "Won't fix"...