Oracle 10g: Special characters are not correctly returned 30 minutes after each Apache restart

Dear all, I'm noticing a very strange problem with my Apache/PHP/Oracle installation. Imediatelly after an Apache restart, it all works OK. But, ~30 minutes later, all the special characters (namely, portuguese accentuated characters) obtained from the DB disappear and are replaced by other chars like "?". It seems to be a PHP-Oracle interface problem, given that all the characters are always OK when the connection is made through TOAD. The variables ORACLE_HOME e NLS_LANG are defined with the following values: ORACLE_HOME=/export/ORACLE/OraHome1 NLS_LANG=American_America.WE8ISO8859P15 Does anyone have a clue on what it's happening? My system: Apache 2.0.52 + PHP 4.3.11 + Oracle 10g (through OCI8) Thanks in advance. Cheers, Paulo Sousa