Appending empty content causes the bubble to grow for no reason

This can be easily triggered with this script:

#!/usr/bin/python
from gi.repository import Notify
from time import sleep

Notify.init(Append None")

for i in range(10):
    n = Notify.Notification.new("Append to me", "")
    n.set_hint_string("append", "true")
    n.show()
    sleep(1)