Select low performance on temporary table and hight performance on no temporary table

Hi,
On RDBMS 10.2.0.5 we have low performance when we run a select on temporary table but we replace the temporary table with no temporary table
the result performance are better.

Details :

CREATE GLOBAL TEMPORARY TABLE "XLA"."XLA_REPORT_BALANCES_GT"
   (	"LEDGER_ID" NUMBER(15,0),....

sqlplus apps

insert into xla_report_balances_gt (.....) select from ........;

14038 rows created.

--- result 1select on temporary  table xla_report_balances_gt ( no statistique on this temporary table and full acces table xla_report_balances_gt ) :

select count(*)
................. from ...... XLA_REPORT_BALANCES_GT
union .....
from .... XLA_REPORT_BALANCES_GT
....;

 COUNT(*)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
----------                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
1389


call     count       cpu    elapsed       disk      query    current        rows