It is not a bug, it is a trial of a new User Interface. What you are seeing is a Beta trial of that Welcome page. Only some users are seeing it and not everybody. That's what Beta trials are about - to evaluate/check something in the real world by giving it to a limited group of users first before a full roll-out. It may well be changed before it is fully released to everybody. See this: https://community.ccleaner.com/topic/64278-welcome-back-to-ccleaner-professional/page/2/#c