System Identification Tool: unstable poles and zeroes?

Hi,

I am using the System Identification Tool for estimating a transfer function.

At the Estimation Options there is no check (and i am not able to check) at 'Allow unstable models'. But in my result of the discrete -time model i got poles and zeroes in the right and left half with a magnitude above 1. That indicates that the model is unstable. Now I am confused and asking for help.

Greets