There's no need for it, and it just means the plasmoid displays completely nonsense out-of-date data.
A quick update on this.
Presence is no longer saved to a config. \o/
NickName and Avatar still are, so effectively all setting them in the plasmoid does is update a config file and reads from it - and it doesn't actually represent anything on the network.
Imho global nicknames and global avatars simply don't work in practice, and therefore it should be killed to death.
This will be eliminated with the new changes to the presence plasmoid
The plasmoid was pretty much rewritten and lost the popup part. Since this is no more an issue, I'm closing it.