Thank you for contacting us.
I am not able to reproduce this problem with Sitefinity 4.0, so I assume that it appears only in the Products module. I will log this bug in our system for fixing.
By design, if you open one published item and schedule it to publish in the future, the item will not be unpublished. The assumption is that you are creating a newer version of the content and you want it published in the future.
As we received various feedback on this dialog we decided to improve its behavior. In the future, when changing the date of publication, you will be able to choose whether you want the item to be unpublished or not.
the Telerik team
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