When an exception is managed by Seam, configured in pages.xml, it's logged if the parameter "log='true'" is present.
This doesn't work for exceptions raised during a page action call: the exception is correctly handled as described in pages.xml, but it is never logged, ignoring the "log" attribute.
To try it:
1) Create a standard seam-gen project.
2) Create a component with an action that has "raise new Exception()" in his body.
3) Associate that action to a commandButton: the exception is logged.
4) Associate the same action to a page action: the exception is not logged anymore.