Why is [P.PROJECT_MANAGER] working in a custom portlet instead of [PROJ.PROJECT_MANAGER]?

[P.PROJECT_MANAGER] is referenced from a filter field and is referring to the alias defined in the main sql statement eg:
SELECT ...e.PROP_PROJECT_MANAGER PROJECT_MANAGER
where PROJECT_MANAGER is an alias column name. To refer to this alias, use "P." before it. This is typically how custom parameters are referred to.