I'm not an expert on php cake, but simple installation + test + documentation on .. http://book.cakephp.org/view/1584/Error-logging assumes that when your debug file is disabled to 0, your log is still continues to keep a log of warnings and fatal errors, so for full debugging you may also need to make the logging false.
Configure::write('log', false);
Extract: errors are logged when Configure :: write ('debug', 0); Will only log warnings and fatal errors. Configure :: write ('log', false); will disable error logging when debug = 0.
Also in the base .php controller (there is no handleError code in libs / controller / controller.php - was this added by your developers?)
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