mailcap configuration in zsh can't open .bk files

[vinurs <haiyuan.vinurs@xxxxxxxxx>]

Hi all,
I wrote
application/pdf; vinurs-pdf %s ;
in my .mailcap file, vinurs-pdf is a function that can open pdf files;

In zsh configuration file:
# MIME system
autoload -U zsh-mime-setup
zsh-mime-setup

then in zsh, I can open pdf files, but ,when I mv test.pdf to test.pdf.bk,
It can not be opened.
I use file --mime-type test.pdf.bk, It shows:
test.pdf.bk: application/pdf

Why this happens? How can I configure that zsh can open test.pdf.bk files.