Vindicators' axes are invisible when inside a team

I just update my version into 16w40a. I want to check my Vindicator guard which guards my home and when I spawn a hostile mob, their axes are gone! I spawn non-team Vindicator and his axe is visible. I kill the team Vindicator and I spawn it again and add into a team, and their axes are gone again! Does anyone know why this happens? Sorry for my bad English.