User blog comment:Arachne sama/Shinigami Skills Heredity/@comment-8295743-20130615003956/@comment-650772-20130617160541

Engetsu and Zangetsu could be the similar due to the hollow White absorbing some of Isshins Shinigami powers during their fight (in the real world or inside Masaki) or a trace of Engetsu remaining on White after the battle (a bit like when Ulquiorra injured inchigo and the wound was covered in Ulquiorra's sprital power) and since we know White fused itself with Ichigos unwakened Shinigami powers.

the trace of Engetsu inside White could have changed Ichigos powers slightly to make it more similar to Isshins then it would have been otherwise