[ghorrocks]

So, setting coeff loops to unity might work as Picard Iteration Method, don´t it?

Why do you think that? I have no idea what a Picard method is (and I don't have time to read you reference) but I know certain bad things happen with only a single coeff loop iteration - for instance I know the second order component of your time differencing only starts taking effect on the second iteration. So you are really running first order time differencing, and a very poorly converged one at that.

So I think it highly unlikely you are getting anything useful out of the simulation by limiting it to 1 coeff loop.

I do not understand your comment that when it runs to convergence each time step the conclusions are the same. If it runs to convergence then the extrapolation or previous time step option should not matter. They should both converge to the same result, but probably with different number of coeff loops to get there.