missmatch between dbms_space.unused_space and dbms_space.space_usage

Hi,

I'm running some tests on oracle database 12.2, i create a table insert rows and run dbms_space.unused_space and dbms_space.space_usage and numbers reported dont match.

1) create table test (a number, b varchar2(50)) tablespace users;

insert into test values (1,null);

commit;

2) run dbms_space.space_usage and got:

Total number of blocks that are unformatted: 0

Number of blocks that has at least 0 to 25% free space: 0

Number of blocks that has at least 25 to 50% free space: 0

Number of blocks that has at least 50 to 75% free space: 0

Number of blocks that has at least 75 to 100% free space: 5

Total number of blocks that are full in the segment: 0