pg_attribute always grow...

Is there any reason why pg_attribute could always grow ( size in
relpages... ) even if number of tuples don't grow...
The indexes pg_attribute_relid_attnam_index and
pg_attribute_relid_attnum_index grow and I don't see any way to vacuum them
without restarting postgres with -O and -P options and launching REINDEX
command.
Could it be due to the fact that I create and drop many temporary tables in
stored procedures ?
Please help!!!!

Thanks

Patrick Fiche
email : patrick.fiche@aqsacom.com
tél : 01 69 29 36 18