I loaded some of the pages I created in VSD. Found a couple of errors, and corrected them
when I reloaded, some of the images and buttons duplicated themselves

How do I make it stop? How did this happen? How do I avoid doing it again?

If you are using the inbuilt FTP do a resink, it will rectify remove and update

Also you cannot edit the pages of a VSD site outside of VSD and still use VSD to edit it later. VSD does not have any import capabilities so it does not know you added things to the pages externally and it will always overwrite them and sometimes have strange things like this happen too. Not sure if you were editing outside the program, just letting you know in case you were.