Hi,
I've noticed that plasma notifications are no more displayed in 4.5+ when using fullscreen applications. In my case it's smplayer, some other guy on this forum mentioned vlc.

In fact, I don't mind that notifications are not displayed because I don't like being disturbed during movies anyway, but on my computer the "hidden" notifications under the video layer cause that the video becomes almost unwatchable... noticeable tearing, fps dropdown... When the notification disappears the video playback returns to normal but it's annoying. I would like to either display notifications properly or disable them completely.

Would you recommend anything to solve my problem?

In this case, the notification is actually shown, but the video player window is simply on top of it, which causes the graphics card to encounter issues, causing the drop in fps, etc. I have seen this myself in KDE Trunk.

I suggest you file a bug report as KDE should simply not show notifications at all (but still have them available from the notifications item in the tray)

Similar bug has already been posted so I just added my experience with smplayer. I hope this will be fixed in future versions of KDE