In kubuntu 14.10 the notifications were stored under notification applet for certain timeout period. So if the notification comes when the screen is locked, you can still read the notification.

In Kubuntu 15.04, certain notifications do not seem to go under notification applet. They pop up as standalone notification for 5 seconds, then they disappear.

This can confirmed when using notify-send program.

Reproducible: Always

Steps to Reproduce:
1.  install libnotify-bin
2. run $notify-send abc 123
3. Observe standalone pop up notification, click Notifications applet - observe it says - No new notifications

Actual Results:  
notifications are missed outside of 5 seconds period

Expected Results:  
notifications are listed under the Notification applet.