If you have an illustrator file open and resave it with a new name - when you then export that file as a PNG it keeps the name that you previously used - not the new saved name. When exporting I have to manually change the name to be the new name I have just given the file. Very annoying when you have to create numerous files off of one original document which you need to keep exporting as a PNG. Even more annoying is when you have exported the file and it is saving over the previous one you created because it has the previous name.