As part of some testing we were doing, we found that PHP's OCI8 extension had a bug in the way it used Oracle's statement caching. The fix is already in CVS and will be generally available in PHP 5.2.4. After a short period for you to send me comments, Antony Dovgal will also build a new PECL snapshot of OCI8.
He explains the issue, a problem attributed to the switching of a "hard pause" and "soft pause" when the script caching connects to the Oracle database server. This caching feature is enabled by adding an "oci8.statement_cache_size" value in your php.ini file (and has a default size of 20).
If you've been having issues with this request caching and want to get the fix right away, grab it from the CVS. Otherwise, keep an eye out for PHP 5.2.4 coming soon to correct the issue.