I wonder why these two codes show difference results:

use sales in 0 alias sales
select sales
mkey='003333'
disp PK for inv=mkey
use in sales

result:
--------
0001
0002
0045
0046

use sales in 0 alias sales
select sales
mkey='003333'
seek mkey order inv
scan while inv=mkey
    disp PK
endscan
use in sales

result:
-------
0001
0002


thanks for the help