Before 1.6, when you exported a selected element (including a screen), you got the standard OS X save dialog with a name field. You now have something more akin to export screens as graphic for exporting a selected element. However, the old way was really helpful for replacing existing images, as I could simply click on the existing image to give my export the same name. This was especially helpful when replacing just one of multiple screens that had previously been exported with prepended numbers.
Therefore, I request that if you are only exporting one element, you should either see the standard OS X dialog, or that if you click an existing file, the name of the element you are exporting changes in the list below the file system browser.
This issue would also be alleviated somewhat if prepended numbers were tied to the screen itself and not exported images.