pgstatindex

Hi all,
I have been watching this  field (index_size) , and see probable bug on size .
anybody may explain me  how fix it?
 select * from pgstatindex('micromedicao.xfk8_consumo_historico');
 version | tree_level | index_size       | root_block_no | internal_pages | leaf_pages  | empty_pages | deleted_pages | avg_leaf_density | leaf_fragmentation
---------+------------+-------------+---------------+----------------+------------+-------------+---------------+------------------+--------------------
          2 |             3 | -1332748288 |         81517       |           1219     |     360379 |                   0 |                    0 |                 78.69 |              16.22

Size of xfk8_consumo_historico on database = 2825MB

one more dought about avg_leaf_density , what's this represent?


Thanks