Notification should display for a minimum time
Some times notification banners are removed just a few milliseconds after they where shown, probably because they became irrelevant really quickly. This leads to annoying flash in screen. I think they should stay for at least a specific timeout or at least finish the animation before getting removed.
One my machine this can be seen when switching between wifi networks. The no network connection notification shows up just for a split second and then gets removed since the computer reconnected to the new wifi.