My finding of the day while I did a clean install on my MacBook Pro:
In OS X Mavericks, Apple started to cache plist files, which results in replacing a plist file manually has no effect until the cache is reloaded automatically. If you open the application which uses this plist file to early, it overwrites your copied file with the old/cached one.
Now you can reload the plist file manually:
defaults read [bundle identifier] # f.ex. for Jitsi defaults read org.jitsi.plist # Full path works too defaults read /Users/username/Library/Preferences/org.jitsi.plist
Or delete the cached one (Not tested myself!):
defaults delete org.jitsi.plist