LIKE In Stored Proc Returns Too Much

I am using SQL Server 2005 Developer on XP Home.
I have the following in one "New Query" window.


use test_01;

go

create table test_tbl_01 (

fname nvarchar(30),

lname nvarchar(30),

phone nvarchar(30),

another_field nvarchar(30));

go

insert into test_tbl_01 (fname, lname, phone, another_field)

values ('Susan', 'Johnstone', '555-0123', 'Some other data');

insert into test_tbl_01 (fname, lname, phone, another_field)

values ('Steven', 'Stonewall', '555-0124', 'More filler data');

insert into test_tbl_01 (fname, lname, phone, another_field)

values ('Bob', 'Otherguy', '555-0125', 'Just some text');

insert into test_tbl_01 (fname, lname, phone, another_field)

values ('Fred', 'Johnson', '555-6666', 'What ev');

insert into test_tbl_01 (fname, lname, phone, another_field)

values ('Carol', 'Jackson', '555-5432', 'You go girl!');

go

create procedure test_sp_01 @LName nvarchar

as

select *

from test_tbl_01 tt

where tt.lname like @LName + '%';

go

exec test_sp_01 @LName = 'John';



The result is:

Susan Johnstone 555-0123 Some other data
Fred Johnson 555-6666 What ev
Carol Jackson 555-5432 You go girl!

Why does the result include Carol Jackson? I expect that it should only include the two John....

More importantly, how can I get it to inlude only Susan Johnstone and Fred Johnson?

Thanks,

Gregory