Sorting when "*" is the initial character

I encountered what looks like unusually sorting behavior, and I'm wondering if
anyone can tell me if this is supposted to happen (and then if so, why) or if
this is a bug:

CREATE TABLE sample_table
(
account_id varchar(4),
account_name varchar(25)
)
WITHOUT OIDS;

INSERT INTO sample_table VALUES ('100', 'First account');
INSERT INTO sample_table VALUES ('110', 'Second account');
INSERT INTO sample_table VALUES ('120', 'Third account');
INSERT INTO sample_table VALUES ('*125', 'Fourth account');
INSERT INTO sample_table VALUES ('*115', 'Fifth account');

SELECT * FROM sample_table ORDER BY 1;

account_id,account_name
100,First account
110,Second account
*115,Fifth account
120,Third account
*125,Fourth account

I would expect to see

account_id,account_name
*115,Fifth account
*125,Fourth account
100,First account
110,Second account
120,Third account