To take a step in that direction, I think there's a setting where you can change the accuracy level at which it turns the satellite green. If you really lower that and it is a GPS issue then it'll do what he's talking about on the other systems. If right now you're allowing it to steer once it's converged below say 12" then it's going to let you steer up to that error. If you had that down at say 3" then if this is a digi issue and it's accuracy is off for a split second then it'll kick out your steering and give you messages on the screen. (is it doing that now or just auto steering you off the good line?) 

And 2nd, to the OP.....you're saying at for example 3:48pm yesterday both of your systems did the same jump at the same time? In different fields? (or whatever day and time)