EM wave Phase change by reflection

kvblake2003@yahoo.com

I think I read that from Maxwell's eqautions it follows that by
reflection of an EM wave on the boundary between two media the
reflected beam (wave) undergoes a phase change of PI or 180 grad
(lambda/2) independent of the media, incidence angle or the percentage
of transmition. But for a beam splitter I read in some textbooks that
the phase change is PI/2 or 90 grad (lambda/4) for the reflected beam.
What is then right? If there is a difference (PI---PI/2) than why?