You have raised an interesting issue

I have followed your example exactly.
Same block size, same table creation command and here are my results


1 select segment_name,sum(blocks),(bytes/1024) from dba_extents group by segment_name,bytes
2* having segment_name = 'TEST'
3 /

SEGMENT_NA SUM(BLOCKS) (BYTES/1024)
---------- ----------- ------------
TEST 16 128

I am confused, can anyone shed light on this