Download links don't work with epub files.

The download link looks good.
The downloaded file has the size it should.
But it isn’t ientical to the source file and doesn’t work.

For example:

$ ll sample.epub [= downloaded file]
-rw-r–r– 1 gp gp 498797 19. Nov 23:29 sample.epub
$ ll tmp/sample.epub [= source file]
-rw-r–r– 1 gp gp 498797 18. Nov 22:12 tmp/sample.epub
$ diff sample.epub tmp/sample.epub
Binary files sample.epub and tmp/sample.epub are different.
$ [files have same size and name but are different, download file does not work.]