Permalink enabled, some non-existing urls redirect to home page

I enabled permalink, using “/%year%/%monthnum%/%postname%/”.
Nginx is my server, with this line in conf:
try_files $uri $uri/ /blog/index.php$is_args$args;

And I found something strange while looking at nginx’s access.log:
with “/phpmyadmin/wp-admin/whatever/file.js”, the guy got 200 – my home page.
Then I played around and found:
“/whatever/wp-admin[/whatever]” –> home page

okay, it doesn’t hurt, but I think it’s totally nonsense.

Can someone explain why this happens and how can I fix this?