user nginx;
worker_processes 1;

error_log /var/log/nginx/error.log warn;
pid /var/run/nginx.pid;

events {
worker_connections 1024;
}

http {
include /etc/nginx/mime.types;
default_type application/octet-stream;

# LET'S LOG $request_method #
log_format main '$request_method $remote_addr - $remote_user [$time_local] "$request" '
'$status $body_bytes_sent "$http_referer" '
'"$http_user_agent" "$http_x_forwarded_for"';

#HERE IS WHAT MAKES A BUG#
error_page 405 /error.html;

access_log /var/log/nginx/access.log main;

sendfile on;
#tcp_nopush on;

keepalive_timeout 65;

#gzip on;

server {
listen 80;

if ($request_method != GET) {
return 405;
}

location / {
root /etc/nginx/www;
}
}

}

What we get:
1)
curl -X POST localhost
log:
GET 127.0.0.1 - - [30/Apr/2014:10:55:03 +0400] "POST / HTTP/1.1" 405 0 "-" "curl/7.26.0" "-"

2)
curl -X TRACE localhost
log:
GET 127.0.0.1 - - [30/Apr/2014:10:55:10 +0400] "TRACE / HTTP/1.1" 405 0 "-" "curl/7.26.0" "-"

3)
curl -X PUT localhost
log:
GET 127.0.0.1 - - [30/Apr/2014:10:55:18 +0400] "PUT / HTTP/1.1" 405 0 "-" "curl/7.26.0" "-"

Let's disable "if":
1) curl -X POST localhost
GET 127.0.0.1 - - [30/Apr/2014:10:58:48 +0400] "POST / HTTP/1.1" 405 0 "-" "curl/7.26.0" "-"
2) curl -X TRACE localhost
GET 127.0.0.1 - - [30/Apr/2014:10:59:12 +0400] "TRACE / HTTP/1.1" 405 0 "-" "curl/7.26.0" "-"
3) curl -X PUT localhost
GET 127.0.0.1 - - [30/Apr/2014:10:59:38 +0400] "PUT / HTTP/1.1" 405 0 "-" "curl/7.26.0" "-"

Let's disable "error_page 405 /error.html;"
1) curl -X POST localhost
POST 127.0.0.1 - - [30/Apr/2014:11:00:43 +0400] "POST / HTTP/1.1" 405 172 "-" "curl/7.26.0" "-"
2) curl -X TRACE localhost
TRACE 127.0.0.1 - - [30/Apr/2014:11:01:02 +0400] "TRACE / HTTP/1.1" 405 172 "-" "curl/7.26.0" "-"
3) curl -X PUT localhost
PUT 127.0.0.1 - - [30/Apr/2014:11:01:16 +0400] "PUT / HTTP/1.1" 405 172 "-" "curl/7.26.0" "-"

So it seems that error_page 405 /error.html rewrites $request_method