I noticed that the application cannot rename a file if there is already one present with the new name.
It is asking for a confirmation to overwrite the existing file, but it does not, after selecting "Yes": the file name does not change in the app, and if the existing file, having the new target name, is opened, its contents is unchanged.
This is the only case which I have noticed that renaming does not work in: if there is no file to overwrite, renaming is successful.
Version 6.5.1 (Unicode)
Built on 2013 Nov 3 at 23:14:16