In our project, we use 6.1 EE and ext plugin. We are overriding three core portlets, we're using liferay-portlet-ext.xml to redefine some preferences.
We are keeping the same <struts-path /> for all three portlets. When portal starts up, we get those three warning messages in log:
11:48:34,950 WARN [PortletLocalServiceImpl:1145] Duplicate struts path journal
11:48:34,951 WARN [PortletLocalServiceImpl:1145] Duplicate struts path journal_content
11:48:34,951 WARN [PortletLocalServiceImpl:1145] Duplicate struts path login
PortletLocalServiceImpl.initEAR() reads first the original liferay-portlet.xml, adds all struts paths to Map (strutsPath -> portletId), then reads liferay-portlet-ext.xml and warns that the same struts path is already being used. Maybe the warning should be given only when the portletId differs as that's perhaps motive for the warning in log – to prevent two different portlets use the same struts-path.