  Currently is argued that the best method of determining the neutron star (NS)
fundamental properties is by measuring the {\it gravitational redshift} ($z$)
of spectral lines produced in the star photosphere. Measurement of $z$ at the
star surface provides a unique insight on the NS mass-to-radius relation and
thus on its equation of state (EoS), which reflects the physics of the strong
interaction between particles making up the star. Evidence for such a
measurement has been provided quite recently by Cottam, Paerels & Mendez
(2002), and also by Sanwal et {\it al.} (2002). Here we argue that although the
quoted observations are undisputed for canonical pulsars, they could be
misidentified if the NS is endowed with a super strong $B$ as in the so-called
magnetars (Duncan & Thompson 1992) and strange quark magnetars (Zhang 2002), as
in the spectral line discovered by Ibrahim et {\it al.} (2002;2003). The source
of this new "confusion" redshift is related to nonlinear electrodynamics
(NLEDs) effects.
