Most of the notifications don't save at the the notification widget. example: notify-send "Test" "Test" even with `critical` urgency. but.. it only saved there if the expiration time is 0 .. i.e it lasts for ever.
Thanks for the report That's by design, only notifications marked as "persistent" (what -t 0 does) are persisted. *** This bug has been marked as a duplicate of bug 342260 ***