User blog comment:Xilinoc/Ch. 541 - THE BLADE AND ME 2/@comment-3230060-20130613145316/@comment-6943043-20130614195151

for the second and third parts, i think that when (fake) zangetsu uses bankai, i think that zanpakuto spirits have full control over the blade's powers. that may be why he becomes so young and handsome, because shinigami only can use at least a fraction of their zanpakuto, even if they use their true power. also, when ichi used FGT, his shinigami powers (h/ichigo) were lost but his quincy powers ((fake) zangetsu) were already present, they hadn't yet "awakened".

this is however, JUST A THEORY.