FreeBSD has had different semantics here for ~20 years: https://github.com/freebsd/freebsd/commit/e4e8fec98ae986357c...

I wish I could find the discussion around that commit.

It'll only start throwing away dirty buffers if the device actually goes away: https://github.com/freebsd/freebsd/commit/46b5afe7b1ae0ee655...