What prevents rotation to this pin constraint?

Hello, I sometimes encounter problems like this. in the assembly I have attached,  I have a fixed part (gorund.prt) then a part  free  to rotate around its axis pin.prt (by manually rotating pin.prt it is in fact free to rotate), 

then I added pivot2.prt, it is fixed with mate constraint on pin.it and should follow the rotation of  pin.it but this does not happen, and it also blocks the rotation of pin.it.What prevents rotation? and how I can remedy it?