With no fanfare or warning (or even a note on the help page), exporting a design sheet will save your design.
If you erase parts that you do not want exported, this will erase them from your design PERMANENTLY.
At a minimum, the program should warn you and let you stop the process before it destroys design information.
A better solution should be to give the user a choice to save or not to save.
You can bring your idea here: