In KDE4, if there's an application blocks logout/shutdown, e.g. unsaved kwrite, plasma will still be there until real shutdown starts.
In Plasma 5, plasma will exit immediately when other application are still blocking the logout procedure. This might leave user a uneasy environment to do their pre-shutdown stuff. 

Reproducible: Always

Steps to Reproduce:
1. Open kwrite and edit some thing, don't save it.
2. Try to logout the system

Actual Results:  
Plasma closed and kwrite ask you about "save the unsaved documents"

Expected Results:  
Plasma doesn't close until you do something with kwrite dialog