I would suggest that you are trying to schedule a content item or page that is already published. In this scenario the desired content will be marked as scheduled but it will appear, because it is already published. In this case you have to unpublish the content first and then you can schedule it without any problems.
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items