[Zope] standard_error_message not being used?

I am experiencing a bit of oddness - I customized standard_error_message in the zope root, yet errors are still displayed with the default standard_error_message. It's like it's using some internal standard_error_message. There are no other standard_error_message files flying around. What could be causing this? Zope 2.5.1 binary (py 2.1.3), on Red Hat 6.1