Thanks for the reply. The auto aim engages with out pressing RMB when the reticle is on the target. So when the shot is fired if playing beek a poo the shot will aim for centre of tank so hits rock or earth. It happens so fast that I do not have time to disengage before the shot is taken.
Then if I do use auto aim by pressing RMB once I have take one shot on auto aim the auto aim disengages.
I have tried various setting both on PC and in game settings different mouse in different ports. Also in safe mode.
It still activates sometime I do get one or two games before this starts.