Thread:Rappy/@comment-28349469-20150602102452/@comment-26479628-20150602131315

There could be a few reasons:

If the MediaWiki:Welcome-user page is set to "lastest", then the welcome messsage will switch to Staff after a certain amount of time/inactivity from the admins (60 days).

Also, if it's set to "staff", then all welcomes will be from a Staff member.

See more at Help:Welcome Tool.