Steve,

When publishing you'll get asked to store the file locally.
But if you open the project later on and you change things on your page,the newly used media get's added to the project export folder,It doesn't delete unused files.
In a way this makes sense but if you forget to delete the unused files from the export folder all the files get uploaded again.
Hence the filesize

Maybe an alert for the storing in local folder at every publish,now it only shows once.

Hans