BUG #14909: nextval() bug

The following bug has been logged on the website:

Bug reference: 14909
Logged by: Max Rys
Email address: personal(at)rysmax(dot)com
PostgreSQL version: 10.1
Operating system: macOS 10.12.6
Description:

I run this simple queries on PostgeSQL 9.6 and 10.1:

DROP TABLE IF EXISTS "user";
CREATE TABLE "user" (
id serial primary key not null,
email varchar(64) not null
);
INSERT INTO "user" (id, email) VALUES ('1', 'admin(at)example(dot)com');
INSERT INTO "user" (id, email) VALUES ('2', 'user(at)example(dot)com');

All done without errors.

When i try to run the query bellow:

INSERT INTO "user" (email) VALUES ('test(at)example(dot)com');

and got the next error in pgAdmin and from the PHP:

ERROR: duplicate key value violates unique constraint "user_pkey"
DETAIL: Key (id)=(1) already exists.

but when i try to run this query 2 times the query executed without errors
on 3rd time.

I think this is a bug in nextval() function.