PHP Error logging

Hello, I currently have a strange issue where we are seeing 'random errors' being displayed to end users. What I find most interesting is that in the php.ini file we have the following error settings. error_reporting = E_ALL & ~E_NOTICE display_errors = Off display_startup_errors = Off log_errors = On log_errors_max_len = 1024 ignore_repeated_errors = Off track_errors = Off I thought that if we had dislay_errors = Off then end users should never see errors displayed on the web page. However at apparently random times we do still see errors being reported, its not consistent at all. To give a better idea of the problem we have 8 web servers, they all run an identical copy of the site which is stored on a common netapp nfs filer. At apparently random times we see that 1 out of 8 servers will reported strange errors like 'use of undefined constant' or 'Undefined variable'. What's most strange about these errors is that if the code was faulty wouldn't we expect to see the errors on all web servers? and secondly wouldn't we expect to see the errors constantly rather than at apparently random intervals? The php.ini files have a modify time of mid 2010 and yet this problem has only started in the last few weeks. Has anyone else experienced similar problems in the past and if so what was the root cause? Regards, Jimmy