Why does a 400 error occur when using the % symbol in a url?

Question

PHP

Why does a 400 error occur when using the % symbol in a url?
Links as an example, you don't have to click ;)
http://www.main.com/test% returns:
Bad Request
Your browser sent a request that this server could not understand.
http://www.main.com/test%test gives:
400 Bad Request
nginx/1.7.4
If you use % after ? everything is fine

RewriteEngine on
Options All -Indexes

RewriteCond %{HTTP_HOST} ^main.com
RewriteRule (.*) http://www.main.com/$1 [R=301,L]

RewriteBase /
RewriteCond %{REQUEST_FILENAME} -s [OR]
RewriteCond %{REQUEST_FILENAME} -l [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^resource/(.*)$ resource/$1 [L]
RewriteRule ^.*$ [NC,L]
RewriteRule ^.*$ index.php [NC,L]

Answer 1

Doctor, when I do this, it hurts. - Don't do that

Because the special character .

Answer 2

% is a prefix that must be followed by a numeric character code.
? it is a separator between URL and parameters.
Read about special characters in URLs