You can fix things by making it explicit where you want the number to appear, by adding [#] to the New Name field:
KP-040316R1-[#].JPG
It should then do what you want.
It looks like this is a bug where renaming things in subfolders does not put the number before the extension if the placement is not explicit. We have some enhancements to the Rename dialog coming which will fix this, put using [#] will also fix things for you now.